Britain being left to destruction, after it's ally had fallen in the south, Churchill, the RAF(Royal Air Force), and the British Army had prepared since the invasion of Poland, and even a month or two before then, when Britain knew there had been something fishy about Hitler's movements. Hitler's goal was to knock out every ally in the world, so that his other plans, would become successful.
In weeks before the invasion of Britain, Britain acknowledged the German might, and knew what the Germans could bring to their country. Already planned and prepared, with all of British might, they were ready to give all they had to stop the Germans and down grade they're German numbers.
July 16, 1940, Hitler ordered the preparations for the invasion of Britain, therefore calling it operation Sealion. On August 13, 1940, German bombers, and fighters stormed the skies of Britain. By next week Germany tried it's hardest to destroy and cripple the RAF. By the August 24-September 6 the Germans became closest to victory. On September 7, hundreds of German bombers and there fighter escorts, headed to London. For the next 76 nights London was bombed.
By September 15, the climax of the Battle of Britain had begun. On that same day 185 Luftwaffe or German aircraft were shot down. The British had held there own well, and on September 17, Hitler postponed the major assault for another day. Hitler had much important things to do other than bothering with Britain. Britain had found hope that the German Army will have it's down fall in the years to come. Which did happen in the Summer of 1942 till 1944. Pictures of London are the effects of German bombing.
I find this a changing point in the war. Germany's first failed attempt, but was still successful. Many lives were taken do to German bombing throughout Britain, but mostly in London. In my opinion Britain's first victory and it's hardest fight against Germany.
Booth, Owen, and John Walton. The Illustrated History of World War II. Edison, NJ: Chartwell, 1998. Print.