Which country chose to join Hitler?

Well czechodlovakia this country joined sides with hitler

Czechoslovakia was invaded and annexed by Hitler, who argued that the high number of Germans living in a region of Czechoslovakia known as the Sudetenland justified his actions. But the Czechs strongly resisted German invasion, so I wouldn't say they "chose to join" him.

Countries that DID voluntarily ally with Hitler included Italy and Japan, as well as the Soviet Union (until Hitler turned on Stalin). Hungary was also part of the Axis Powers, and until 1944 Bulgaria and Romania were, too.

Finland also had an uncomfortable alliance with the Nazis, but only because they were desperately and heroically trying to fend off a Soviet invasion during what is now called the Winter War. Since the Nazis were the enemies of the Soviets, the Finnish people entered into a hesitant alliance with the Nazis in order to save their homeland.