"Divide and Conquer" is one of seven films in Frank Capra's "Why We Fight" 1940's series.
It begins with Britain and France's declaration of war on Germany after Hitler's invasion of Poland. The film covers the Nazi capture of Denmark and Norway, steps necessary to mount a future attack on Britain, then describes in detail Hitler's strategy as he conquers Luxembourg, Belgium and the Netherlands. Special attention is paid to Nazi atrocities. Dead and injured children are shown en masse and the film explains how the bombing of Rotterdam leads to "thirty thousand men, women and children killed in ninety minutes."
The narrator tells how the Luftwaffe bombs small villages so that refugees clog the highways, and how it uses precision machine gun fire to herd the survivors toward the allied armies, who find their progress severely constrained as a result. An American military officer details the Nazi plan for an invasion of France, which Hitler conquers in just over a month. The Germans bludgeon the French armies into surrender, then "enslave" much of the local population to service the German military regime.