In the Atlantic, the year 1942 was difficult : German submaries sank 500 American merchant and troop ships. Threatening the supply to Britain.
Due to better US/UK technology and strategy, by the end of 1942, Germany was losing more ships than it could build in the Atlantic Front
In the Eastern Fron, there was a Soviet war effort against the Nazi Germany.
In 1942, in the eastern front, the Red Army stopped the German advancement at Stalingrad followed by the Soviet advance to Berlin.
On the Eastern Front, the U.S. didn't send troops but provided material support and aerial bombings
FDR wanted to invade France as early as 1943. Churchill convinced him to start with North Africa in late 1942. The victory in Africa served as a foothold for the invasion of Europe, starting with Italy.
SIcily fell in August1943.Mussolini was overthrown and an armistice was signed on September, 3 1943
British and American forces instituted "saturation bombing", killing 300,000 civilians and destroying 5 million homes in the european front.
The Allied massed more than 3 million soldiers (15 different nationalities) in England
In May 1942, the U.S. Navy intercepted and destroyed a Japanese troop convoy planning an attack on Australia at Coral Sea.
In June 1942 : the battle of Midway broke the back of the Japanese Navy
Creation of the "Leapfrog strategy" : invading strategic islands
February-March 1945 : Battle of Iwo Jiwa (Pacific front)