World War 1, 1914-18, also called the Great War, conflict, chiefly in Europe, among most of the world's great powers. On one side were the Allies (chiefly France, Britain, Russia, and the U.S.); on the other were the Central Powers (Germany, AustriaHungary, and Turkey).
Prominent among the war's causes were the imperialist, territorial, and economic rivalries of the great powers. The German empire in particular was determined to establish itself as the preeminent power on the Continent. The Germans were also intent on challenging the naval superiority of Britain. However, it was rampant nationalismespecially evident in the AustroHungarian empirethat furnished the immediate cause of hostilities. On June 28, 1914, Archduke Francis Ferdinand, heir apparent to the AustroHungarian throne, was assassinated at Sarajevo by a Serbian nationalist. One month later, after its humiliating demands were refused, AustriaHungary declared war on Serbia. Other declarations of war followed quickly, and soon every major power in Europe was in the war.
On the Western Front, the Germans smashed through Belgium, advanced on Paris, and approached the English Channel. After the first battles of the Marne and Ypres, however, the Germans became stalled. Grueling trench warfare and the use of poison gas began all along the front, and for the next three years the battle lines remained virtually stationary despite huge casualties at Verdun and in the Somme offensive during 1916.
On the Eastern Front, the Central Powers were more successful. The Germans defeated (Aug-Sept. 1914) the Russians at Tannenberg and the Masurian Lakes. Serbia and Montenegro fell by the end of 1915. In the south, the Italian campaigns were inconclusive, though they benefited the Allied cause by keeping large numbers of Austrian troops tied down there. In Turkey, the Allies' ambitious Gallipolli Campaign (1915), an attempt to force Turkey out of the war, was a costly failure. In the Middle East, T.E. Lawrence stirred Arab revolt against Turkey.
U.S. neutrality had been threatened since 1915, when the British ship Lusitania was sunk. By 1917 unrestricted German submarine warfare had caused the U.S. to enter the war on the side of the Allies. An American Expeditionary Force, commanded by Gen. Pershing, landed in France and saw its first action at ChateauThierry (June 1917).
In Mar. 1918 the new Soviet government signed the Treaty of BrestLitovsk with the Central Powers. The Germans were stopped just short of Paris in the second battle of the Marne, and an Allied counteroffensive was successful. The Turkish and Austro-Hungarian empires, disintegrating from within, surrendered to the Allies, as did Bulgaria. After revolution erupted in Germany, the armistice was signed on Nov. 11, 1918.
The Treaty of Versailles and the other treaties that ended the war changed the face of Europe and the Middle East. Four great empiresGermany, Austria-Hungary, Russia, and Turkeyhad disappeared by the end of the war. Replacing them were governments ranging from monarchies and sheikhdoms through constitutional republics to the Marxist socialist state of the USSR.
The war itself had been one of the bloodiest in history, without a single decisive battle. A total of 65 million men and women had served in the armies and navies; an estimated 10 million persons had been killed and double that number wounded. Such statistics contributed to a general revulsion against war, leading many to put their trust in multinational disarmament pacts and in the newly formed League of Nations.
World War II 1939-45, conflict involving every major power in the world. On one side were the Allies (chiefly Great Britain, the U.S., and the Soviet Union) and on the other side the Axis powers (Germany, Japan, and Italy).
The conflict resulted from the rise of totalitarian, militaristic regimes in Germany, Japan, and Italy after World War 1. Partly responsible also were the humiliating peace treaties forced on Germany after that war and the worldwide economic disorders brought on by the Great Depression of the 1930s. In Asia the second Sino-Japanese War (1931) was followed by continuing Japanese aggression. In 1936 Benito Mussolini conquered Ethiopia for Italy, thereby dramatizing the ineffectuality of the League of Nations. French and British appeasement of Adolf Hitler's Nazi regime in Germany culminated in the Munch Pact (1938), which sacrificed much of Czechoslovakia to Germany. France and Britain, nevertheless, began to rearm and to offer guarantees to other potential victims of German aggression, notably Poland. In Aug. 1939 Germany and the Soviet Union, previously bitter enemies, concluded a nonaggression pact, thus freeing Hitler to invade Poland (Sept. 1). France and Britain immediately declared war on Germany, officially beginning World War 11.
The Germans won a quick victory in Poland, and went on to occupy Norway and Denmark in 1940. In May they overran the Low Countries, broke into France, and swept to the English Channel. On June 22 France surrendered (although a Free French force continued to fight). Britain, under Prime Min. Winston Churchill, was left to fight alone. The Battle of Britain (Aug.-Oct. 1940), Germany's attempt to bomb Britain into submission, was the only German failure of the war's early years. Axis land operations continued in N Africa and in the Balkans, where Greece and Yugoslavia were occupied.
On June 22, 1941, Germany invaded the Soviet Union, bringing that nation, under Premier Joseph Stalin, into the war.
Meanwhile, the U.S., under Pres. F.D. Roosevelt, was drawing closer to the Allies. On Dec. 7, 1941, Japan attacked Pearl Harbor, bringing the U.S. into the war.
But Axis successes continued. By 1942 Japan had conquered the Philippines, many other Pacific islands, and all of Southeast Asia; German forces in the Soviet Union reached Stalingrad and the Caucasus; Rommel seemed about to take Cairo; and German submarines were threatening to wipe out Allied shipping.
Late in 1942, however, the Allies began to rally. In N Africa, British Gen. Montgomery's rout of Rommel at Alamein (Oct. 1942; see North Africa, Campaigns in), and the landing of U.S. troops in Algeria, resulted in Allied victory in Africa. The Allies conquered Sicily and S Italy, and Italy surrendered (Sept. 1943). In the Pacific, U.S. forces won (1942) the naval battles of the Coral Sea and Midway, landed on Guadalcanal, and began the island-hopping strategy that by 1945 had won back the Philippines and brought a striking force to Japan's doorstep at Iwo Jima and Okinawa.
The German surrender at Stalingrad (1943; see Volgograd) was followed by a Soviet offensive that by 1944 had taken Russian troops deep into Poland, Hungary, and the Balkans.
In the battle of the Atlantic, the German submarine fleet was virtually destroyed.
German resistance in N Italy was stubborn, however, especially at Cassino and Anzio. On June 6, 1944 (known thereafter as D Day), the final Allied campaign began with the landing of troops in Normandy. In August a second force landed in S France. By late 1944 Belgium and France were liberated, and the war had been carried into the Netherlands and Germany. Allied bombing, meanwhile, was destroying German industrial centers.
In Dec. 1944 the Germans staged a last-ditch counterattack in the Ardennes [forest in Belgium]. By Jan. 1945, however, the Allies were continuing their drive into Germany. The Russians had conquered E Germany to the Oder. On March 7 the Western allies broke through the Siegfried Line, crossed the Rhine, and overran W Germany. In Apr. 1945, after Hitler's suicide, German resistance collapsed, and on May 7, 1945, Germany surrendered unconditionally.
The Allies now turned their attention to the Pacific. The Soviet Union declared war on Japan and occupied Manchuria. In Aug. 1945, while U.S. troops were preparing to invade Japan's home islands, Pres. Truman ordered the dropping of the Atomic Bomb on Hiroshima and Nagasaki. Japan announced its surrender on Aug. 14, 1945, thereby bringing to an end the costliest war in history.