World War I began on July 28, 1914, when Austria-Hungary declared war on Serbia. This seemingly small conflict between two countries spread rapidly: soon, Germany, Russia, Great Britain, and France were all drawn into the war, largely because they were involved in treatiesthat obligated them to defend certain other nations. Western and eastern fronts quickly opened along the borders of Germany and Austria-Hungary.

THE WESTERN AND EASTERN FRONTS
The first month of combat consisted of bold attacks and rapid troop movements on both fronts. In the west, Germany attacked first Belgium and then France. In the east, Russia attacked both Germany and Austria-Hungary. In the south, Austria-Hungary attacked Serbia. Following the Battle of the Marne(September 5–9, 1914), the western front became entrenched in central France and remained that way for the rest of the war. The fronts in the east also gradually locked into place.

THE OTTOMAN EMPIRE

Late in 1914, the Ottoman Empire was brought into the fray as well, after Germany tricked Russia into thinking that Turkey had attacked it. As a result, much of 1915 was dominated by Allied actions against the Ottomans in the Mediterranean. First, Britain and France launched a failed attack on the Dardanelles. This campaign was followed by the British invasion of the Gallipoli Peninsula. Britain also launched a separate campaign against the Turks in Mesopotamia. Although the British had some successes in Mesopotamia, the Gallipoli campaign and the attacks on the Dardanelles resulted in British defeats.

TRENCH WARFARE

The middle part of the war, 1916 and 1917, was dominated by continued trench warfare in both the east and the west. Soldiers fought from dug-in positions, striking at each other with machine guns, heavy artillery, and chemical weapons. Though soldiers died by the millions in brutal conditions, neither side had any substantive success or gained any advantage.

THE UNITED STATES’ ENTRANCE AND RUSSIA’S EXIT

Despite the stalemate on both fronts in Europe, two important developments in the war occurred in 1917. In early April, the United States, angered by attacks upon its ships in the Atlantic, declared war on Germany. Then, in November, the Bolshevik Revolution prompted Russia to pull out of the war.

THE END OF THE WAR AND ARMISTICE

Although both sides launched renewed offensives in 1918 in an all-or-nothing effort to win the war, both efforts failed. The fighting between exhausted, demoralized troops continued to plod along until the Germans lost a number of individual battles and very gradually began to fall back. A deadly outbreak of influenza, meanwhile, took heavy tolls on soldiers of both sides. Eventually, the governments of both Germany and Austria-Hungary began to lose control as both countries experienced multiple mutinies from within their military structures.The war ended in the late fall of 1918, after the member countries of the Central Powers signed armistice agreements one by one. Germany was the last, signing its armistice on November 11, 1918. As a result of these agreements, Austria-Hungary was broken up into several smaller countries. Germany, under the Treaty of Versailles, was severely punished with hefty economic reparations, territorial losses, and strict limits on its rights to develop militarily.

GERMANY AFTER THE WAR

Many historians, in hindsight, believe that the Allies were excessive in their punishment of Germany and that the harsh Treaty of Versailles actually planted the seeds of World War II, rather than foster peace. The treaty’s declaration that Germany was entirely to blame for the war was a blatant untruth that humiliated the German people. Furthermore, the treaty imposed steep war reparationspayments on Germany, meant to force the country to bear the financial burden of the war. Although Germany ended up paying only a small percentage of the reparations it was supposed to make, it was already stretched financially thin by the war, and the additional economic burden caused enormous resentment. Ultimately, extremist groups, such as the Nazi Party, were able to exploit this humiliation and resentment and take political control of the country in the decades following.

GERMAN AGGRESSION

The war in Europe began in September 1939, when Germany, under Chancellor Adolf Hitler, invaded Poland. Britain and France responded by declaring war on Germany but took little action over the following months. In 1940, Germany launched its next initiative by attacking Denmark and Norway, followed shortly thereafter by attacks on Belgium, the Netherlands, and France. All of these nations were conquered rapidly.

THE BATTLE OF BRITAIN

Later in the summer of 1940, Germany launched a further attack on Britain, this time exclusively from the air. The Battle of Britain was Germany’s first military failure, as the German air force, the Luftwaffe, was never able to overcome Britain’s Royal Air Force.

GREECE AND NORTH AFRICA

As Hitler plotted his next steps, Italy, an ally of Germany, expanded the war even further by invading Greece and North Africa. The Greek campaign was a failure, and Germany was forced to come to Italy’s assistance in early 1941.

THE USSR

Later in 1941, Germany began its most ambitious action yet, by invading the Soviet Union. Although the Germans initially made swift progress and advanced deep into the Russian heartland, the invasion of the USSR would prove to be the downfall of Germany’s war effort. The country was just too big, and although Russia’s initial resistance was weak, the nation’s strength and determination, combined with its brutal winters, would eventually be more than the German army could overcome. In 1943, after the battles of Stalingrad and Kursk, Germany was forced into a full-scale retreat. During the course of 1944, the Germans were slowly but steadily forced completely out of Soviet territory, after which the Russians pursued them across eastern Europe and into Germany itself in 1945.

THE NORMANDY INVASION

In June 1944, British and American forces launched the D-Day invasion, landing in German-occupied France via the coast of Normandy.Soon the German army was forced into retreat from that side as well. Thus, by early 1945, Allied forces were closing in on Germany from both east and west. The Soviets were the first to reach the German capital of Berlin, and Germany surrendered in May 1945, shortly after the suicide of Adolf Hitler.

The Pacific Theater

PEARL HARBOR

The war in the Pacific began on December 7, 1941, when warplanes from Japan launched a surprise attack on the U.S. Navy base at Pearl Harbor, Hawaii. By this time, Japan had already been at war with China for several years and had seized the Chinese territory of Manchuria. After the Pearl Harbor attack, Japan began a massive campaign of expansion throughout the Southeast Asia–Pacific region.

THE U.S. ENTRANCE AND BATTLE OF MIDWAY

Although the Pearl Harbor attack provoked a declaration of war by the United States on Japan the very next day, it would be several months before U.S. forces would get seriously involved militarily. In late spring of 1942, the United States and Japan engaged in a series of naval battles, climaxing in the Battle of Midway on June 3–6, 1942, in which Japan suffered a catastrophic defeat.

THE SOLOMON ISLANDS AND GUADALCANAL

For the next year, the United States engaged Japan in a protracted struggle for the Solomon Islands, which lay near vital Allied shipping routes. Between August 1942 and February 1943, Allied forces carried out an invasion on the island of Guadalcanal—the beginning of a long series of Allied offensives that would eventually force the Japanese out of the Solomons and then pursue them from various other Pacific island chains that the Japanese had earlier seized. In the meantime, British and Indian forces were combating Japanese troops in Burma.

THE APPROACH TO JAPAN

Fighting continued throughout the Pacific in 1944 and early 1945, including major battles at Leyte, Iwo Jima, and Okinawa. By the late spring of 1945, most of Japan’s conquests had been liberated, and Allied forces were closing in on the Japanese home islands. As they neared Japan proper, the Allies began heavy bombing campaigns against major Japanese cities, including Tokyo. This process continued through the summer of 1945 until finally, in early August, the United States dropped two atomic bombs on the cities of Hiroshima and Nagasaki. Stunned by the unexpected devastation, Japan surrendered a few days later.