What caused the Blitz to take place?

Answer 1

It started August 25, 1940, when a lost German pilot accidentally bombed central London. The British sent a retaliatory bombing strike to Berlin the next night. Hitler was incensed and issued orders to launch a merciless bombing campaign against London. On September 7, the London Blitz began. The fragile diplomatic tent protecting citizens collapsed, and both the Allies and Axis began to attack and terrorize each other's citizens.

Londoners were treated to almost nightly bombing raids by Luftwaffe Heinkel aircraft. The Germans were aided in their targeting with early radar guidance systems, named X-Gerate and Knickebein. But compared to the Allied bombings of Germany later in the war, these were small excursions because of the limited carrying capacities of the airplanes. On an average night, 200 German bombers would attack, dropping about 300 tons of bombs. Forty thousand British were killed and many historic buildings and cathedrals destroyed. Faulty intelligence told Luftwaffe planners that the citizens of Britain were feeling the pressure of the attacks and repeated German bombing would soon lead to victory.

Hope this helped :)

This info was pasted and slightly altered from : http://www.centennialofflight.gov/essay/Air_Power/Bombing/AP27.htm

All credit goes to Pamela Feltus