Well, let's look at that. Germany Conquered the low countries, Poland, France, Norway, Denmark, Greece and Yugoslavia.
The countries that voluntarily joined were Austria (Sorry, the Anchluss was very popular in Austria) Slovakia, Romania, Bulgaria, Hungary, Finland, Italy. Mostly because they all hoped to get in on some of the action and gain territory. (Most of them ended up losing territory instead.)
Yugoslavia is instructive... They initially joined the Axis, had an anti-Axis Coup. Hitler invaded them on the way to Greece (they were just in the way) and established a puppet government in Croatia called the Ustase. The Ustase were so vicious in their mistreatment of Jews and other minorities that even the Nazis were shocked.
right wingers from France, Norway and Denmarck were happy to join special Wehrmacht units to fight the Bolsheviks in Russia. And when it came to the Jews, everyone in Europe has happy to help in wiping them out.