Essential Events Between 1900 and 1945
Learn how two world wars and other critical developments reshaped global affairs in the first half of the twentieth century.
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When the USS Maine exploded in Cuban waters on February 15, 1898, and killed 266 Americans, sensational news reports blaming Spain whipped up public support for U.S. intervention in Cuba’s war for independence from its Spanish colonizers. But what then-U.S. Secretary of State John Hay referred to as a “splendid little war” was more than a simple matchup between two major powers over their interests in the Americas. Rather, the conflict clearly signaled the United States’ growing ambitions on the world stage and closer to home—in the Caribbean and its countries. Nearly three hundred thousand Americans, including Theodore Roosevelt’s Rough Riders, answered President William McKinley’s call for troops. After months of fighting, Cuba emerged with its independence, and the United States emerged with much of Spain’s colonial empire in the Caribbean and Pacific, including Guam, the Philippines, and Puerto Rico. Additionally, the Platt Amendment, which the United States insisted be part of the Cuban constitution, designated Guantanamo Bay as a permanent U.S. military base.
When the Russo-Japanese War broke out in 1904, Japan and Russia had already been tussling for decades over control of Manchuria, a resource-rich region in Northeast Asia. The Japanese emerged victorious and proved the country capable of trumping Western military might—a rarity in the nineteenth century. This milestone helped cement Japan’s reputation as a growing military and colonial power, one that was treated as an equal—diplomatically—by Western powers. It also weakened the prestige of czarist Russia and nearly led to revolution, and dampened Russia’s imperial ambitions in East Asia. By the conflict’s close, Japan controlled much of southern Manchuria and the region’s valuable mining and railroad interests; by 1910, the island nation had fulfilled further imperial ambitions by annexing Korea.
The late nineteenth and early twentieth centuries were periods of rapid technological innovation. The automobile, radio, and television—invented in 1886, 1901, and 1927 respectively—would all go on to change the course of history. But it was the launch of the British warship HMS Dreadnought that brought together a series of new technologies that sparked the first arms race of the twentieth century. The ship, a feat of naval engineering, featured twelve-inch guns, submerged torpedo tubes, and steam turbine engines, which had never been brought together before. A coinciding arms race on land produced long range weapons, chemical gas, and difficult-to-reverse military mobilizations. This frenzied militarization among the world’s most powerful countries ultimately helped provide the kindling for World War I.
On June 28, 1914, Archduke Franz Ferdinand, heir to the throne of Austria-Hungary, was assassinated, an event that famously kicked off World War I. But why did the assassination of one man cause the whole world to dive into conflict? The short version: it’s complicated. The longer version requires looking at the long-term forces that led to mutual hostility and suspicion among European powers—including nationalism, competition for empires and markets, an arms race, mobilization plans, and values such as militarism. Alliance systems which were meant to act as a deterrent to maintain a balance of power ended by dragging their members into conflicts. These forces produced a war that would turn what most thought would be a quick “home by the holidays” military engagement into a deadly four-year, continent-spanning conflict between the Central Powers (Austria-Hungary, Germany, and the Ottoman Empire) and the Allied Powers (Britain, France, Russia, and eventually Italy and the United States, and many more such as China and Japan) that ultimately killed approximately nine million soldiers.
After gold was discovered in California in 1848, Americans were desperate for a faster way to get from coast to coast. This desire only increased when Hawaii and the Philippines became U.S. territories, highlighting the need for a shortcut between the Atlantic and Pacific Oceans that would allow warships and commercial vessels to get from one U.S. coast to another without rounding South America. By encouraging and supporting Panama’s push for independence from Colombia, the United States ultimately succeeded in building the Panama Canal, which opened to traffic in 1914. The United States could now sail far more easily and safely between its two shores, allowing the country to integrate its domestic economy and continue on its path toward becoming a global economic and military power.
From the use of tanks and submarines, to the widespread deployment of fighter pilots and new military uniforms with steel helmets, World War I was truly a conflict of military firsts. Sadly, this also marked the first time chemical weapons and machine guns were used on such a massive scale. Throughout the war, the machine gun resulted in massive casualties without requiring soldiers to even aim at a specific target. During the Second Battle of Ypres, the German army opened thousands of cylinders of chlorine gas in the trenches along its defensive perimeter in Belgium. The results were immediate. A wall of gas killed more than six thousand Algerian and French soldiers and harmed thousands more. The war marked the first time in modern warfare that an army used weapons of mass destruction, a fateful milestone in the world’s military history.
Anticipating a victory, two senior diplomats—Britain’s Sir Mark Sykes and France’s Francois Georges Picot—met in secret at the height of World War I to preemptively divvy up their countries’ spheres of influence within the Ottoman Empire, which included present-day Turkey and most of the Arab Middle East. When Russia (post-Bolshevik Revolution) leaked news of the meeting, outrage ensued due to Britain’s clear intention to withdraw its promised support for an independent Arab kingdom if the Arab population rose against the Ottomans. Despite the leak, the terms of the Sykes-Picot Agreement, which eventually included Italy and Russia, were largely codified after the war with the Treaty of Sèvres. Both Britain and France went on to draw new borders that had less to do with the people who lived in those areas and more to do with what the World War I victors needed to fuel their empires: oil and access to Mediterranean seaports, respectively.
Despite its growing global power, the United States sought to stay out of World War I. Its resolve was tested in 1915 when German submarines attacked a British ocean liner, the RMS Lusitania, killing nearly 1,200 people, including over 100 Americans. The ensuing outcry led Germany to cease its submarine activity against civilian shipping, in a bid to keep the United States neutral and on the sidelines. However, in 1917, Britain intercepted a note sent by Germany to Mexico proposing a military alliance possibly to include Japan as well should the United States enter World War I—a proposal sweetened with a promise to help Mexico reclaim territory it had lost during the Mexican-American War. The Zimmerman Telegram, coupled with past grievances and, above all, Germany's decision to resume unrestricted submarine warfare in 1917, led a reluctant United States into the war. By July 1918, one million American troops had arrived in Europe to fight with the Allied forces; by November, Germany was fatally weakened and the war was over.
After sustaining territorial losses in the early twentieth century and devastating loss of life during World War I, the czarist regime in Russia was severely weakened. In early 1917, a revolution protesting food shortages—started by working-class women and including factory workers and soldiers who deserted—overthrew Tsar Nicholas II and established a provisional democratic government in the country. This kicked off a period of seismic change within Russia that culminated in Vladimir Lenin leading a faction of Communists called the Bolsheviks in a second revolution to overturn the just-installed government. Lenin created the Cheka, or secret police, with the authority to execute those who didn’t comply with his new government’s rules, which included nationalizing private land and factories. By 1918, civil war had engulfed the country and caused it to pull out of World War I as Lenin hoped to consolidate power; five years later, Bolsheviks, now known as the Communist Party of the newly formed Soviet Union, had defeated the so-called “Whites” and controlled most of the former Russian Empire.
Before the turn of the twentieth century, only one country—New Zealand—gave women the right to vote, and it wasn’t until World War I that meaningful strides were made toward granting women this right around the world. The global scale of conflict made it necessary for women to enter the workforce in greater numbers, and the shift highlighted a glaring injustice: that women could work and die for the war, yet they could not vote for it. In 1906, Finnish women were the first Europeans to win the right to vote, followed in short order by Norweigan women (1913), Russian women (1917), and then British women over thirty years old, Canadian women of some ethnicities and races, and German women (1918). In the United States, the passage of the Nineteenth Amendment in 1920 gave women the right to vote, but for many American men and women, racist laws intended to thwart their political participation would remain in place for decades to come.
At 11 a.m. on the eleventh day of the eleventh month of 1918, World War I came to a halt—a day that would come to be known as Armistice Day. The Allies emerged victorious, though they had little to celebrate. During four years of war, over ten million civilians and roughly nine million soldiers died, and more than double that number were left wounded, some injured for life. In the conflict’s final year, a deadly virus later known as the Spanish Flu coursed through the world, ultimately infecting about one-third of the planet and taking upwards of fifty million lives. World War I was unprecedented in many ways, but particularly in the death, carnage, and environmental destruction it caused. Known at the time as the war to end all wars, World War I proved to be the opposite, planting the seeds for another devastating conflict just two decades later.
Two months after World War I ended, world leaders convened in Paris to discuss the terms of peace. The war’s victors—led by the United States, Britain, and France—dominated conversations regarding terms of peace and multiple treaties resulted, most notably the Treaty of Versailles, which forced major territorial concessions from Germany and limited its army and navy. Most consequentially, it forced Germany to accept responsibility for the war and to pay reparations for damages done to its enemies, which humiliated and infuriated the German people and would fuel the rise of Adolf Hitler in the coming years. The Treaty of Versailles also established the League of Nations to serve as an international forum based on the premise of collective security to avoid renewed conflict. The organization’s effectiveness, however, was limited by several factors, including the United States’ ultimate refusal to join.
Before World War I, the global economy was booming. Technological advances such as the steamship and the telegraph, trade and investment, and the relatively free movement of people without immigration limits—or passports—brought the world closer together than ever before. The postwar world, however, was a different story: countries grew protectionist, and trade and immigration restrictions followed. When the U.S. stock market crashed on October 29, 1929, the Great Depression was already starting to affect countries around the globe. The depression spread to Europe by 1931, pushing many governments toward authoritarian regimes. In Germany, the country’s economy tanked and unemployment soared. Germans were drawn toward radical anti-democratic parties on both the right (Nazis and nationalists) and the left (Communists), which promised solutions. Adolf Hitler would mix this economic desperation with his racist, toxic nationalism to gain and consolidate power and ultimately lead the world into a war more deadly than the first.
The worldwide embrace of post-war protectionism and its ruinous effects on global trade put the island nation of Japan in a particular bind. In response to a growing need for food and oil and other raw materials plus markets, the Japanese invaded Manchuria, the start of an aggressive expansion campaign across East Asia and the Pacific. Though the Japanese promoted the invasion as “independence” for Manchuria, the League of Nations rejected this view and urged Japan to withdraw from the region; it withdrew from the League instead. After Japan went on to invade further parts of China in 1937, war crimes became common. One of the most horrific instances was the Rape of Nanjing, where between one hundred and three hundred thousand people were killed and between twenty and eighty thousand women sexually assaulted.
By 1932, six million people out of a labor force of approximately twenty five million people in Germany were unemployed. As the Great Depression caused economic pain for many Germans, the ideas of Adolf Hitler and his Nazi party—which promised to fix Germany’s broken economic system and make Germany a great power again—began to resonate. The party initially downplayed Hitler’s extreme views on race and used people’s fears of communism to drum up electoral support, and by 1933, Hitler was named chancellor of Germany by conservatives in the parliament who thought they could use him. He almost immediately passed legislation allowing himself to centralize power in Germany's government, and by 1934, he had become the supreme leader of the country. By the next year, Hitler had eliminated all other political parties, passed the Nuremberg Laws ending civil liberties for Jewish people in Germany, and begun building up the country’s military in clear violation of the Treaty of Versailles. These actions would culminate as Hitler began his campaign of European expansion and aggression.
For decades, Ethiopia remained independent while European powers colonized its neighbors. However, in 1935, an emboldened Italy led by fascist dictator Benito Mussolini invaded Ethiopia, a member of the League of Nations. The League protested the invasion, but took little action, declining to even close the Suez Canal to Italian ships. Even Italy using mustard gas against both Ethiopian military forces and civilians did little to change the League's hands-off approach. Once again, the ineffectiveness of the League of Nations was on display. By 1936, Italy had annexed Ethiopia and merged the country with Eritrea and Somaliland into a single country known as Italian East Africa. Mussolini then signed on to the Rome-Berlin Axis, formalizing cooperation with Hitler; in 1939, this relationship was strengthened by the signing of the Pact of Steel, which formalized a full military alliance between Fascist Italy and Nazi Germany.
As authoritarian or far-right governments came to power across Europe, a coup in Spain pitted the country’s liberal and leftist Republican government against the Nationalists, a group of fascist rebels led by General Francisco Franco. Britain and France declined to get involved in the resulting civil war, although the Soviet Union supported the Republicans. Franco turned to Germany and Italy for aid, and Italy supplied seventy-five thousand troops, plus pilots and planes. Meanwhile Germany used the conflict to test-run blitzkrieg, or lightning war, a military strategy meant to overwhelm its opponents with coordinated attacks by air and on the ground. Thousands of foreign fighters traveled to Spain to fight against the advance of fascism, yet after three years of bloodshed, the fascists emerged victorious and Franco established himself as dictator. Though Spain did not join the Axis powers (Germany, Italy, and Japan) in World War II, many historians consider the Spanish Civil War as practice for the war.
In the years leading up to World War II, Nazi Germany grew more aggressive both inside and outside its borders. Yet, as Germany institutionalized anti-Semitism at home and annexed Austria, Hitler drew little response from European leaders, who instead tried to accommodate or appease him, in hopes that they could avoid another devastating global conflict. When leaders of Britain, France, Germany, and Italy met in Munich in the late summer of 1938 to discuss Germany’s desire to annex of the Sudetenland, a majority-German region in the newly formed country of Czechoslovakia, Britain and France—once again—declined to stop Germany’s growing aggression. By August 1939, Germany had entered into a nonaggression pact with the Soviet Union, divvying up spheres of influence in Eastern Europe and paving the way for the two countries to invade Poland, which took place weeks later. World War II was in full swing.
With much of Eastern Europe occupied by Nazi Germany and the Soviet Union (the Soviet Union had also invaded Poland and annexed and occupied land in Eastern Europe), Hitler set his sights west, invading France through Belgium, then controlling it. The Germans overwhelmed the French in just six weeks and divided the conquered country in half, occupying the north and setting up a puppet government to rule the south from the city of Vichy. As Germany set its sights on an invasion of their island nation, British air forces emerged successful from the so-called Battle of Britain, which prevented the Germans from dominating the air over Britain and its coastal seas and thus carrying out its invasion. Undeterred, Hitler began a bombing campaign known as the Blitz, in which British cities were attacked every night for eight months and British citizens lived in terror, many sheltering underground at night and emerging in the day to survey the damage done and care for the wounded and dead. The Blitz campaign ended in May 1941, as stiff British resistance persuaded Hitler that his war aims would be better served by turning his attention to the Soviet Union, which he believed had become a greater threat to his ambitions.
As Nazi Germany invaded and overtook much of Eastern Europe, it forced Jewish people into ghettos with terrible living conditions. This repression escalated into organized violence on November 9, 1938—known as the Night of Broken Glass, or Kristallnacht—when Nazi soldiers set fire to synagogues, schools and homes, and sent thirty thousand Jewish people to concentration camps. By late 1941, Nazis were implementing a system Hitler referred to as the “final solution to the Jewish problem” in killing centers designed specifically for mass murder. Over the course of the war, thousands of German citizens and foreign collaborators aided the Nazis as they murdered six million Jews and millions of other persecuted people. After the war, the term genocide—the deliberate harming of a specific group of people—emerged as part of a canon of human rights law to describe this atrocity, which was known as the Holocaust.
As fighting raged in Europe and Asia, U.S. lawmakers remained determined to stay out of World War II. In reality, though, the United States’ Lend-Lease policy, which ultimately distributed more than $45 billion in military supplies to its European and Asian friends, put the United States increasingly on the side of the democratic, anti-Fascist allies. Meanwhile, U.S. embargoes made Japan increasingly desperate for oil and other essential war materials and led to its provocative decision to occupy French Indochina, neighbor to the Philippines, a U.S. territory. As last-ditch negotiations to end the embargoes faltered, Japan launched a surprise attack on a major U.S. military base in Hawaii, killing more than two thousand U.S. soldiers, sinking four U.S. battleships, and destroying hundreds of aircraft. Referring to the December 7, 1941, attack on Pearl Harbor as “a date which will live in infamy,” President Franklin D. Roosevelt asked Congress for a declaration of war against Japan and received it the next day; three days later, Japan’s European allies declared war on the United States thus bringing the United States into the European war as well.
In June 1941, Hitler launched the largest-scale military attack in modern history, deploying three million soldiers against the Soviet Union in violation of the nonaggression pact signed between the two countries in 1939. In early victories, Germany conquered large swathes of territory, taking over half a million prisoners of war within five months. But then the brutal Russian winter arrived. German machines froze and fighting slowed. When it resumed in earnest the following spring, Germans attacked Stalingrad with its eyes on Soviet oil fields to the south. In a battle considered the war’s turning point, the city survived Germany’s onslaught, and the Soviet Union launched a successful counteroffensive. The resulting victory was not without losses: approximately two million people perished during this half-year battle. More Soviet soldiers died in this one siege than American soldiers throughout the whole war; only six percent of the captured German soldiers survived. The beginning of the end of World War II had arrived.
Within hours of their assault on Pearl Harbor, Japanese forces attacked a string of Pacific countries and territories, including Hong Kong, Indonesia/the Dutch East Indies, Malaysia, Singapore, and U.S. territories including the island of Guam and the Philippines. After roughly half a year of Japanese momentum, the United States destroyed several of Japan’s aircraft carriers at the Battle of Midway in June 1942 and went on the offensive, setting its sights on Japanese-controlled Burma, Guadalcanal in the Solomon Islands, and the rest of the Pacific. At the Battle of Guadalcanal, Japan lost two-thirds of its soldiers during a six-month battle it ultimately lost, and in 1943, the United States began a campaign of strategic island-hopping toward the Japanese archipelago. Meanwhile, Japan’s Axis allies had recently faced significant losses in Northern Africa, as British soldiers broke through German and Italian military lines threatening Egypt and the Suez Canal and gained a victory in El Alamein, Egypt. As the Allies gained ground in the Pacific and Northern Africa, the tide of the war began to turn in their favor.
After gains in Eastern Europe, Northern Africa, and the Pacific, the Allied forces sought to relieve pressure on the Soviet Union’s forces attacking Germany from the South and West. In July 1943, the Allies invaded first Sicily signaling the start of the successful Italian campaign. After Mussolini was overthrown, the new government signed an armistice that left Germany isolated. Then, in an effort to liberate France, the Allies stormed the beaches at Normandy with what was the largest shipborne landing in history, augmented by overnight parachute and glider landings, massive air attacks, and naval bombardments. This invasion included more than 150,000 soldiers primarily from the United States, Britain, and Canada and approximately 7,000 naval vessels, leaving the Allies with a hold on Normandy. Subsequent military campaigns moved through France, and by August 1944, Paris was liberated. Meanwhile, the Allies continued their attacks on Germany. In February 1945, at a point where Germany was already weakened, they began a three-day bombing of Dresden, destroying over twelve thousand buildings and leaving approximately twenty-five thousand civilians dead. On May 8, 1945, Germany surrendered, ending World War II in Europe.
Though victory in Europe had been secured, war with Japan raged on. In March 1945, the United States firebombed Tokyo, flattening the city. Approximately one hundred thousand civilians were killed, and one million people were left homeless. Japan’s military leaders refused to surrender. U.S. President Harry S. Truman, seeking to avoid the long and costly fight he believed would follow an armed invasion of Japan, turned to a brand-new weapon: the nuclear bomb. On August 6, 1945, the United States dropped the first of these singularly destructive weapons on the Japanese city of Hiroshima, killing an estimated 80,000 people instantly, and leaving over 120,000 to deal with severe burns and radiation poisoning. When the Japanese did not immediately surrender, the United States dropped another bomb on Nagasaki three days later, killing seventy-four thousand people. On August 15, 1945, the Japanese unconditionally surrendered. World War II, the deadliest conflict in history, had come to an end.