Answer:
Attack on Pearl Harbor - it was important because it started the official U.S. involment in the War.
Creation of the Manhattan project - this secret project led by Robert Oppenheimer consisted in the development of an atomic bomb. It was key for the victory of the American army over the Japanese Empire.
D-Day - It was the day in which the Normandy landings took place. France, at the time controlled by Nazi Germany, was invaded by the American and the British armies through Normandy, a region in Northern France.
Executive order 9066 - this order consisted in the internment of Japanese Americans in concentration camps.
Fall of Berlin (surrender of Germany) - this event marked the end of the war in Europe. The U.S. army could now focus most of its efforts in the Pacific against Japan.
Hiroshima - The first of the two Japanese cities to be struck by atomic bombs.
Lend-lease program - with this program, the U.S. Army mobilized economic and military resources to the Soviet Union, which was, at the time, pratically fighting Nazi Germany on its own.
Nagasaki - the second Japanese city to be struck by an atomic bomb. After this strike, the Japanese Emperor surrendered, and the war ended.
Outbreak of WWII in Europe - the war started in September, 1939, and the U.S. did not get directly involved until December, 1941, however, it was an ally of France and Britain, and gave some support, especially to Britain.
