After the treaty of Versailles Germany was forced to give up its territory’s of Alsace and Lorraine to France and other territory’s and cities to Denmark, Czechoslovakia and Poland
To allow Poland access to sea it was pretty much cut in half.
This paired with other restrictions like the limitation of Germany’s army to 100.000 troops, ban on importing and exporting of weapons, and the ban on having aircrafts and submarines and to pay war reparations would lead to rise of fascism (nazism) that would than lead to World War 2