The instability created in Europe by the First World War (1914-18) set the stage for another international conflict–World War II–which broke out two decades later and would prove even more devastating. Rising to power in an economically and politically unstable Germany, Adolf Hitler Adolf Hitler, leader of the Nazi Party, rearmed the nation and signed strategic treaties with Italy and Japan to further his ambitions of world domination. Hitler’s invasion of Poland in September 1939 drove Great Britain and France to declare war on Germany, marking the beginning of World War II. Over the next six years, the conflict would take more lives and destroy more land and property around the globe than any previous war.
The devastation of the Great War (as World War I was known at the time) had greatly destabilized Europe, and in many respects World War II grew out of issues left unresolved by that earlier conflict. In particular, political and economic instability in Germany, and lingering resentment over the harsh terms imposed by the Versailles Treaty, fueled the rise to power of Adolf Hitler and National Socialist German Workers’ Party, abbreviated as NSDAP in German and the Nazi Party in English..

After becoming Chancellor of Germany in 1933, Hitler swiftly consolidated power, anointing himself Führer (supreme leader) in 1934. Obsessed with the idea of the superiority of the “pure” German race, which he called “Aryan,” Hitler believed that war was the only way to gain the necessary “Lebensraum,” or living space, for the German race to expand. In the mid-1930s, he secretly began the rearmament of Germany, a violation of the Versailles Treaty. After signing alliances with Italy and Japan against the Soviet Union, Hitler sent troops to occupy Austria in 1938 and the following year annexed Czechoslovakia. Hitler’s open aggression went unchecked, as the United States and Soviet Union were concentrated on internal politics at the time, and neither France nor Britain (the two other nations most devastated by the Great War) were eager for confrontation.

On September 17, Soviet troops invaded Poland from the east. Under attack from both sides, Poland fell quickly, and by early 1940 Germany and the Soviet Union had divided control over the nation, according to a secret protocol appended to the Nonaggression Pact. Stalin’s forces then moved to occupy the Baltic States (Estonia, Latvia and Lithuania) and defeated a resistant Finland in the Russo-Finish War. During the six months following the invasion of Poland, the lack of action on the part of Germany and the Allies in the west led to talk in the news media of a “phony war.” At sea, however, the British and German navies faced off in heated battle, and lethal German U-boat submarines struck at merchant shipping bound for Britain, sinking more than 100 vessels in the first four months of World War II.
On April 9, 1940, Germany simultaneously invaded Norway and occupied Denmark, and the war began in earnest. On May 10, German forces swept through Belgium and the Netherlands in what became known as “blitzkrieg,” or lightning war. Three days later, Hitler’s troops crossed the Meuse River and struck French forces at Sedan, located at the northern end of the Maginot Line, an elaborate chain of fortifications constructed after World War I and considered an impenetrable defensive barrier.

In fact, the Germans broke through the line with their tanks and planes and continued to the rear, rendering it useless. The British Expeditionary Force (BEF) was evacuated by sea from Dunkirk in late May, while in the south French forces mounted a doomed resistance. With France on the verge of collapse, Italy’s fascist dictator Benito Mussolini formed an alliance with Hitler, the Pact of Steel, and Italy declared war against France and Britain on June 10.
On June 14, German forces entered Paris; a new government formed by Marshal Philippe Petain (France’s hero of World War I) requested an armistice two nights later. France was subsequently divided into two zones, one under German military occupation and the other under Petain’s government, installed at Vichy France. Hitler now turned his attention to Britain, which had the defensive advantage of being separated from the Continent by the English Channel.

To pave the way for an amphibious invasion (dubbed Operation Sea Lion), German planes bombed Britain extensively beginning in September 1940 until May 1941, known as the Blitz, including night raids on London and other industrial centers that caused heavy civilian casualties and damage. The Royal Air Force (RAF) eventually defeated the Luftwaffe (German Air Force) in the Battle of Britain, and Hitler postponed his plans to invade. With Britain’s defensive resources pushed to the limit, Prime Minister Winston Churchill began receiving crucial aid from the U.S. under the Lend-Lease Act, passed by Congress in early 1941.
In North Africa, British and American forces had defeated the Italians and Germans by 1943. An Allied invasion of Sicily and Italy followed, and Mussolini’s government fell in July 1943, though Allied fighting against the Germans in Italy would continue until 1945.
On the Eastern Front, a Soviet counteroffensive launched in November 1942 ended the bloody Battle of Stalingrad, which had seen some of the fiercest combat of World War II. The approach of winter, along with dwindling food and medical supplies, spelled the end for German troops there, and the last of them surrendered on January 31, 1943.

World War II proved to be the deadliest international conflict in history, taking the lives of 60 to 80 million people, including 6 million Jews who died at the hands of the Nazis during the Holocaust. Civilians made up an estimated 50-55 million deaths from the war, while military comprised 21 to 25 million of those lost during the war. Millions more were injured, and still more lost their homes and property.
The legacy of the war would include the spread of communism from the Soviet Union into eastern Europe as well as its eventual triumph in China, and the global shift in power from Europe to two rival superpowers–the United States and the Soviet Union–that would soon face off against each other in the Cold War.

World War II exposed a glaring paradox within the United States Armed Forces. Although more than 1 million African Americans served in the war to defeat Nazism and fascism, they did so in segregated units. The same discriminatory Jim Crow policies that were rampant in American society were reinforced by the U.S. military. Black servicemen rarely saw combat and were largely relegated to labor and supply units that were commanded by white officers.