When writing a response to this question, you should consider a range of reasons that led them to entering the war. One of the main reasons is explained below:
The hatred for the Treat of Versailles: Hitler along with the rest of Germany felt that the Treaty was unfair and a rather harsh punishment on Germany. They felt that they had been 'stabbed in the back' because of the penalties imposed on them through the terms of the Treaty. For example, they were forced to limit their army to a token army; they had to pay reparations (millions!); they lost land; and they had to take them blame for starting WW1.
This most definitely was a main contributing factor in causing the Second World War.