10 Astounding World War 2 Facts You Didn't Know

In the years approaching the full-on war, Spain suffered a fascist revolt. Hoping to court a new ally, Germany and Italy backed the fascist revolutionaries led by Francisco Franco by sending arms, supplies, and eventually troops. The future Axis powers saw Spain as a fantastic testing ground for their new arms and tactics.

Ultimately they found massed tank battles to be a complete failure due to the Iberian mountain ranges, and likewise aerial bombardment didn't achieve much success against the sparsely grouped Spanish forces on the slopes. However, the German Condor Legion, a battalion specializing in combined air-and-ground operations realized that if you flew over top of flat areas you could drop a whole bunch of bombs on them all at once in a line.

It was especially effective, they discovered, on tightly-packed civilian locations, such as the small market town of Guernica. In only a single day of bombing the Condor Legion killed over 200 civilians, with many hundreds more wounded. They repeated these attacks within the city of Barcelona to even greater effect - killing a total of 1300 Spaniards and wounding several thousand more in only three days of bombing.

Carpet bombing would, of course, become standard fare on all sides for the rest of the war (and every war since).