1) Great Britain and France entered the fighting because they had pledged to aid Poland.
2)The Soviet Union joined the allies in June 22 because Germany invaded the Soviet Union violating a 1939 non agression pact between the two countries.
3) Japan bombed The U.S military bases Pearl Harbor and Hawaii, The United States declared war on Japan and Joined the Allies.
4)Italy invaded France after joining the war as an ally of Germany.
5)The first major allied victory in witch U.S was involved was the D-Day In June 6th 1944 when the allies attacked German forces in France.
6)the fighting takes place mostly in Europe and in Asia
7)Two atomic bombs were dropped by The United States on two cities In Japan Nagasaki and Hiroshima In April 1945.
8) 9 months after D-Day Germany surrendered.
9) I think V - J Day was celebrated on September 2 nd because the formal surrender ceremony takes place on this day.
10) about 45 millions civilian were killed in World War II