Causes of D-Day

During WWII, the Germans used Blitzkrieg (lightening war) to win many battles. However, this kind of war requires efficient supplies and specialized communication systems, which later on drained the Germans out of supply. The Germans lost a battle against Russia and the eastern line was broken. As a result, Russia asked Britain and America to form a new battlefield in Western Europe. At the same time, Italian army surrendered after losing against Britain and America, which helped Britain and America to concentrate its arm force. After Casablanca conference and Tehran conference, Britain and America reached an agreement to open up the second battlefield in Western Europe.