Why did germany enter ww2?

they didn't enter but started ww2 by invading Poland 1939 to gain there lost territory from WW1. France and Britain then declared war on Germany

Germany initially became part of the first World War due to the treaty it had with Austria-Hungary, which had declared war on Serbia due to the assassination of Archduke Franz Ferdinand. France and Russia were both also party to the war on the Allies side due to Russia's treaty with Serbia and France's treaty with Russia