Great Britain had a major involvement in the development and end of WWII. It was on the side of the Allies and together with France were the first nations that gave front to Hitler after breaking not only the Treaty of Versailles, but also his promise of stop expanding after taking the Sudetenland. It's ability on the naval warfare and strong moral coming from its prime minister, Winston Churchill, it came a time when they were the only ones left on the European Front (after France was quickly overrun by the Nazis), proving Great Britain as a major part on the Allies' victory.
Great Britain took many actions in WWII. Together with France, Great Britain was in charge of supervising the Weimar Republic, making Hitler slowly make changes to the Treaty of Versailles. France and Great Britain took a policy of appeasement towards Germany since they thought their changes didn't mean any harm. Soon after Hitler took Sudetenland, Winston Churchill predicted that Hitler was not to be trust, but his oppinion was not taken to account. That was on the European Front, on the Pacific Front soon after the Nanking Massacre, Great Britain along with the USA applied embargos for Japan not to receive oil.
After Germany's invasion of Poland, two days later France and Great Britain declared war to Germany. In June 22, 1940 France signed armistice with Germany, so Great Britain stood alone against Germany. Hitler tried to invade Great Britain by sending airplanes to bomb it, but it failed causing only that the morale in Great Britain raised up, making it impossible for Hitler to perform the Sea Lion operation. Great stood alone until USA entered the European front eventually winning the war on 1945.
After WWII, Great Britain got a quarter of Germany and a quarter of Berlin. which was later unified with the american and french quarters to form the FRG. Afterwards, Great Britain didn't participate on a big role on the Cold War, but did allign with America's side on the Iron Curtain, a term that was proposed by British Prime Minister, Winston Churchill.
