-Even though the Russian counteroffensives had pushed back Hitler into Europe, he and his allies still controlled the entire mainland of Europe. All except for Spain, Portugal, Switzerland, and Sweden. Those following countries remained neutral.

-Hitler declared war on the United States on December 11, 1941.

-Since 1942 Soviet leader Joseph Stalin had been pressing his allies, U.S. President Franklin D. Roosevelt and British Prime Minister Winston Churchill, to mount a "second front" in the west.

-In January 1944 Eisenhower became supreme Allied commander

-By November 1943, Hitler accepted that it could be ignored no longer, and in Führer Directive 51 he announced that France would be reinforced.

-In January 1944 the Allies also appointed Bernard Law Montgomery as an invasion commander.

-Montgomery's first acts were (1) to demand and get five divisions to make the initial landing and (2) to widen the landing area to include the Orne River estuary and the base of the Cotentin Peninsula.

-The British divisions had been under intensive training since 1942, the American since 1943. Meanwhile, intensive logistic preparations provided, by May 1944, almost 6,500 ships and landing craft, which would land nearly 200,000 vehicles and 600,000 tons of supplies in the first three weeks of the operation.

-The invasion would be supported by more than 13,000 fighter, bomber, and transport aircraft, against which the Luftwaffe (the German air force) was able to deploy fewer than 400 on D-Day. Between April 1 and June 5, 1944, the British and American strategic air forces, deploying 11,000 aircraft, flew 200,000 sorties, dropping 195,000 tons of bombs on French rail centres and road networks as well as German airfields, radar installations, military bases, and coastal artillery batteries.

-Two thousand Allied aircraft were lost in these preliminaries.

-The air campaign was designed not only to disrupt German anti-invasion preparations but also to serve as a deception operation.

-Two-thirds of the bombs were dropped outside the invasion area, in an attempt to persuade the enemy that the landings would be made northeast of the Seine