German rearmament was a policy and practice of rearmament carried out by Germany from 1918 to 1939 in violation of the Treaty of Versailles, which required German disarmament after World War I to prevent it from starting another war. It began on a small, secret, and informal basis shortly after the treaty was signed and was openly and massively expanded after the Nazi Party came to power in 1933.
Under the Weimar Republic, the early steps towards rearmament began with support for paramilitary groups including the Freikorps and Citizens' Defense, although the government banned most such groups by 1921. Secret cooperation between the German military and Soviet Russia began in 1921 and grew to include training in and manufacture of weapons banned by the Versailles Treaty.