The treaty of Versailles imposed harsh provisions on Germany including returning the often disputed region of Alsace- Lorraine to France. Since the Germans did not take part in the conference and when they disagreed to the terms the Allies threatened war again many Germans thought that it was unfair. This allowed the Nazi party to prey on the distrust and anger in the German people and use it to their advantage to gain power. Sorry if it's not entirely clear and if you need more details or examples history.com and britannica.com have good resources and I think Britannica recently updated their article on the Treaty of Versailles.
