Question

number of enlistment cards
which event led to the peak of 3,030,407 enlistments for us military service in 1942?
the blitzkrieg of london by german air forces
the declaraton of war by the soviet union on germany
the attack on the pearl harbor naval base by japan
the discovery of concentration camps in poland

Explanation:

The attack on Pearl Harbor (December 7, 1941) directly led the US to enter World War II. This event galvanized public support and led to a significant increase in military enlistments. The Blitzkrieg of London (1940 - 1941) was a European - theater event that didn't directly involve the US in the same immediate way. The Soviet Union's declaration of war on Germany (1941) was a Soviet action. The discovery of concentration camps in Poland (known more widely later in the war) was a moral shock but not the immediate cause of the 1942 enlistment peak. The Pearl Harbor attack was the catalyst for US full - scale military engagement and thus the enlistment surge.

Answer:

the attack on the Pearl Harbor naval base by Japan