Question

How did the campaigns in North Africa, Sicily, the Atlantic, and in the air help the Allies prepare to defeat Italy and Germany?

Answer 1

For the Atlantic, you would know that it is referring to the Battle of the Atlantic, which involved the U-boat campaign against the British cargo vessels which had aimed to launch a blockade on Britain and it was part of Hitler's plan to starve Britain into submission and surrender.

However, the failure of this in the Atlantic paved the way for the Western Allies (USA & the UK) to launch Operation Overlord which was a large-scale invasion on the beaches of Normandy on 6 June 1944. This allowed the Allies to open up a third front against the Axis (I consider the African campaigns as the 2nd front), and hence put more strain on the German Army (Wehrmacht) and its supply lines, having already suffered heavy losses in the East against the USSR