The Nazi narrative was all about reclaiming what was rightfully the German people's land and resources after they were depressed by the reparations from WWI. It was created to get people behind the party and it worked.

We got involved with Europe's affairs because we made a killing selling them military equipment to blow each other up. Then it started to seem as if the Nazis might take over the continent. To drive this point home, we sold weapons to the Nazis until 1941.

Pearl Harbor happened because we started an oil embargo with Japan.

Vietnam was a proxy war, it's inherently about not letting the enemy gain land or an ally in a certain territory.

There is something to gain behind every aggression and it is usually material and for personal profit to the those initiating it.