World War II was the biggest and deadliest war in history,
involving more than 30 countries. Sparked by the 1939
Nazi invasion of Poland, the war dragged on for six bloody
years until the Allies defeated the Axis powers of Nazi
Germany, Japan and Italy in 1945. Explore the battles,
leaders and atrocities from the war and its impact on
geopolitics and humankind.
When Japanese bombers appeared in the skies over Pearl Harbor on the morning of December
7, 1941, the U.S. military was completely unprepared for the devastating surprise attack, which
dramatically altered the course of World War II, especially in the Pacific theater. But there were
several key reasons for the bombing that, in hindsight, make it seem almost inevitable. Tensions
Began During the Great Depression Before the Pearl Harbor attack, tensions between Japan and
the United States had been mounting for the better part of a decade. The island nation of
Japan, isolated from the rest of the world for much of its history, embarked on a period of
aggressive expansion near the turn of the 20th century. Two successful wars, against China in
1894-95 and the Russo-Japanese War in 1904-05, fueled these ambitions, as did Japan’s
successful participation in World War I (1914-18) alongside the Allies. The Path to Pearl Harbor
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During the Great Depression of the 1930s, Japan sought to solve its economic and demographic
woes by forcing its way into China, starting in 1931 with an invasion of Manchuria. When a
commission appointed by the League of Nations condemned the invasion, Japan withdrew from
the international organization; it would occupy Manchuria until 1945. In July 1937, a clash at
Beijing’s Marco Polo Bridge began another Sino-Japanese war. That December, after Japanese
forces captured Nanjing (Nanking), the capital of the Chinese Nationalist Party, or Guomindang
(Kuomintang), they proceeded to carry out six weeks of mass killings and rapes now infamous as
the Nanjing Massacre.