1 Answer

Officially for the US, from December 7, 1941 to VJ day, the day the Japanese signed the document of surrender aboard the USS Missouri. Sept 2, 1945

President Roosevelt and the England's Prime Mister both realized they needed to stop Hitler sooner, rather than later.

In 1939 England agreed to stand against Hitler and FDR  sent weapon, ships, ammunition, fuel, food etc., to England and Russia via the "Lend Lease Program," which was never a loan or a lease.  They did so to hold Hitter off until the US could get into the war, and we wold have to fight him ere rather than there.

FDR got England to stop selling British oil to Japan to stop its war with China, who they invaded to get coal and iron ore. 

He expected Japan to hit us in the Philippines where MacArthur was with his army.  The Japanese had other ideas, you do not need to fight a starving army.  By destroying our Pacific Fleet at Pear they defeated MacArthur's army, by cutting off all supplier. 

What they did not understand was why the Japanese did not invade our west cost, which was undefended because we lost our Pacific fleet.

After the war the Japanese Admiral was asked that question.  He said, because the US had the worlds largest army reserve.  Four Million armed citizens, who know how to shoot. 

God Bless the Second Amendment