Japan was particularly threatened by the construction of the Pearl Harbor base and the Panama Canal (World pp). On December 7, 1941, Japanese warplanes attacked Pearl Harbor, the largest U.S. naval base in the Pacific, and the following day, the United States declared war on Japan (World pp). Japan also attacked U.S. air bases in the Philippines, and immediately invaded the Philippines and the British Colonies of Hong Kong, Malaya, Borneo and Burma in order to seize the oilfields of the Dutch East Indies (World pp).

A few days later on December 11, 1941, Germany declared war on the United States, although it was not obligated to do so under the 1940 Tripartite Pact, also called the Three-Power Pact, that was signed by Nazi Germany, Fascist Italy and Japan, forming the Axis Powers, and warning the U.S. To remain neutral in the war (World pp). Hitler...

To join the fight in Europe without opposition from Congress or the American people (World pp). Many historians mark this moment as one of the major turning points of the war with Hitler provoking a grand alliance of powerful nations who were capable of waging powerful attacks on both the East and West simultaneously (World pp).
The United Nations was founded in 1945, and to prevent such a devastating war from occurring again to establish peace, the European Coal and Steel Community was born in 1951, the Treaty of Paris, and predecessor of the European Union (World pp).

Works Cited

World War II. http://en.wikipedia.org/wiki/World_War_II