World War I was promised to be the war to end all wars. The Great War was over but an even greater one was looming. In the mid-1930s war was inevitable. After Germany invaded Poland Great Britain responded by declaring war. World War II was in many ways a continuation of disputes that were left unsettled after World War I. 60 million people were killed during the years 1939 -1945 making this war the deadliest conflict in human history. What happened on the front line is what lead Britain to win World War II.