There are many theories about what started World War II. The most popular belief is that Hitler wanted more land to expand Germany. Looking for a reason to start a war and invade Poland, but not wanting it to appear that he instigated it, Hitler staged a polish attack on Germany. This would justify Germany's counter-attack and invasion of Poland.
On August 31, 1939, under Hitler's command and Himmler's ingenuity, a small group of German Nazis dressed in Polish uniforms invaded a German radio station. They left behind a dead prisoner from a concentration camp also dressed in a Polish uniform, making it appear like he died in an attack on the radio station. On September 1, Germany declared war on Poland. Ignoring warnings from Great Britain and France to withdraw their troops from Poland, Germany continued their invasion.
Two days later on September 3, both Great Britain and France declared war on Germany. This series of events started World War II. Later, the war would serve as a mask for Hitler's holocaust and genocide of Nazi's truest enemy, the Jews.
The United States entered the war when Japan attacked Pearl Harbor on December 7, 1941. The very next day, the United States declared war on Japan and on December 11, declared war on Germany.
On June 6, 1944, nearly 150,000 soldiers invaded the beaches of Normandy. D-Day, as it came to be known, was the western Allies largest amphibious invasion in world history. Before the month of June was over, more than 850,000 American, British and Canadian troops would occupy Normandy. U.S. General Dwight D. Eisenhower called the invasion on Normandy "The Great Crusade".
On April 30, 1945, Hitler, along with his long time mistress, committed suicide and approximately one week later; Germany surrendered, putting an end to World War II. The end of World War II was the beginning of an era known as the Cold War which would continue for the next fifty years.
Over 100 million military personnel participated in the war making it the most widespread war in history. Around 72 million people lost their lives including 47 million civilians and 25 million military personnel.
20 million deaths were from war related famine and disease and 4 million prisoners of war died in POW camps. This astronomical death toll would make World War II the deadliest war in history. It was not only profound with the large number of casualties. It was also known as the most costly war, costing approximately one trillion dollars.