The way that World War 2 started was in September 1939. Germany invaded Poland Causing Britain and France to declare war on Germany. The outbreak of war was triggered by Germany's invasion of Poland, but the are more causes of the war which are more complex.
In Germany 1933, Adolf Hitler had became Chancellor of Germany. It was almost immediately when he began secretly building up Germany's army and weapons. By 1934 he increased the size of the army, he began building warships and a German air force. There was also an introduction of compulsory military service. Britain and France were aware of Hitler's actions, but they were also concerned about the rise of Communism in the west and believed that a stronger Germany might help to prevent the spread of it.
In 1936 Hitler ordered German troops to enter the Rhineland. Even though at this time, the German army was not very strong and could have been easily defeated. Unfortunately, neither France nor Britain were not prepared to start yet another war. Hitler also made two important alliances during 1936. The first alliance was called the Rome-Berlin Axis Pact which allied Hitler's Germany with Mussolini's Italy. The second alliance was called the Anti-Comintern Pact and allied Germany with Japan.
The Munich Agreement, was signed by the leaders of Germany, Britain, France and Italy. This agreement stated that the Sudetenland would be returned to Germany and no further territorial claims would be made by Germany. But in 1939, Germany invaded the rest of Czechoslovakia. This invasion broke the terms of the agreement, which helped the cause of WW2.
After the war, Germany was a huge mess. Germany, had to set up peace treaties, countries that had fought with Germany during the war had lost territory and had to pay reparations to the Allies. Germany, was also in debt due to the fact that they had spent a lot of money to try and keep the German war machine running. Overall, Germany had a long way to go to clean up the mess they made.
On April 30, 1945 Adolf Hitler had committed suicide in his bunker. The reason of why he did it was because Germany was on the verge of losing the war. In order to escape future trials and not wanting to accept defeat, he ingested cyanide and shot himself in the head. A week later, Germany had surrendered.