During the early part of the 20th century, the world witnessed two major conflicts: World War I and World War II. The first, which began in 1914, caused a series of international conflicts that led to the collapse of four great imperial dynasties.

The second, which began in 1941, grew out of Japan’s imperial ambitions. Japan’s attack on Pearl Harbor, Hawaii, on December 7, 1941, thrust the United States into another global conflict. The attack sparked a ferocious battle between the two powers. It also aroused Americans’ fighting spirit.

World War I, also known as the Great War, was a global conflict between the world’s major powers. It ended with the Treaty of Versailles, which recognized Germany’s responsibility for the war and forced it to give up its overseas colonies. In return, Germany was forced to pay enormous war reparations.

The Treaty of Versailles was signed on December 11, 1918. It called for Germany to give up 13 percent of its European territory, as well as limiting its army and navy. In addition, it called for reparations to be paid to the war’s winners.

The Treaty of Versailles was a catalyst for the rise of Adolf Hitler in Germany. He had promised his followers to undo the treaty. As a result, Germany re-introduced conscription.

By the end of the war, more than nine to ten million military personnel had been killed. The exact number will never be known.

After the war, the world’s economic system was radically altered. Globalization enabled the production of large quantities of military hardware. It also helped to bind different fronts of conflict. In addition, America’s economic might helped to reinforce the Allies.