Hitler didn't invade any countries. The Nazis did under Hitler's commands. Let's be accurate here.
The Nazis invaded:
Why is a matter of Hitler's words: lebensraum - literally "living room." Lebensraum is additional territory considered by a nation, especially Nazi Germany, to be necessary for national survival or for the expansion of trade. That and the Nazis were taking back what they believed had either been taken from them after WW1 or they had been denied as one German people after the breakup of the various Hapsburg monarchies.
Poland
Hitler first annexed Austria.
czechoslovakia
Poland
he was stupied
Germany never invaded Hitler, Hitler was a human being, not a country.
Belgium
poland
Hitler invaded poland when WW2 started
Austria
Poland
He invaded the country called spell properly