The Blitz of London and other major cities in the UK refers to the period during World War II when London was heavily bombed by the luftwaffe (1940-1941).
42,000 Britons died as a result of the blitz, and over 130,000 homes were vaporised. Hitler also commisioned the V2 to attack.
Although the object of the blitz was to weaken British morale, it served as quite the opposite as Churchill focused his speaches to praising the indefatigueability of the British public, thus strenghtening morale.
With the capture of the radar, and discovery of the german radar patterns the blitz ended. German aircraft could no longer keep accuratly hitting their targets.