On August 24th, 1940, a Luftwaffe pilot became lost on a night bombing mission over England. With fuel running low, he opted to do the prudent thing and drop his bombs over some sparsely inhabited farmland, rather than risk hitting the then forbidden target of London. Unfortunately for the errant pilot, his bombs landed squarely on the blacked-out capital. Enraged by this unsportsmanlike assault on it's civilians, the British retaliated by launching an air raid on Berlin. The very next day, a red-faced Hitler ranted that the criminal terror bombings would be avenged tenfold. He ordered the London Blitz, giving the RAF a much needed respite from the unrelenting attacks on their airfields, and ultimately costing Germany any chance of victory in the Battle of Britain. With the gloves now off, both sides abandoned any attempt to confine their attacks to military targets, and soon bombs were raining indiscriminately over every major city in Europe. And so terror bombing became forever enshrined in the military's strategic dictionary, where it was euphemistically known as "area bombing" by the British, "precision bombing from 30,000 feet" by the USAAF, and "Oh, no, not again" by the Japanese populace. But whatever it was called, the result was invariably a lot of high-explosive falling more or less randomly over populated cities in an effort to convince people not to go work in the factories. Which is sort of ironic, given most people really didn't want to go to work, anyway.
Accidents happened a lot to airplanes during the war, and it was another such accident that helped to shape the destiny of France, which was next on Hitler's hit list following the successful invasion of Poland. Hitler's generals had intended to invade France following a strategy very similar to the original "Schleiffen Plan" of WWI, and probably would have achieved similar results...that is, a stalemate in front of Paris, as they ran head on into the bulk of the Allied armies. However, a plane bearing a low ranking German officer and a copy of the plans for the attack was forced down over France by bad weather and the plans fell into the hands of the French. They completely disregarded them, thinking it was all too easy and probably a trick. The German generals didn't know this, of course, and were forced to consider a new plan, this one put forward by an audacious young general Manstein who advocated driving the bulk of German armor through the densely forested hills of the Ardennes, an area widely regarded by both sides as impassible to armor. Hitler liked the idea, pushed it past the objections of his generals and it eventually became the unexpected strategic master stroke that caught the French napping and led to their ultimate downfall. All because a single airplane crashed at an inopportune moment.
Ironically, Hitler would do the EXACT SAME THING to the Allies four years later at the Battle of the Bulge, this time catching the Americans napping. You'd think someone would have put up a sign up by then.