By that logic, America was not justified in attacking Germany during WWII. Countries have several good reasons to invade other countries. They can come to the

By that logic, America was not justified in attacking Germany during WWII. Countries have several good reasons to invade other countries. They can come to the defense of their allies. Or they can invade to stop genocide, such as in the Kosovo War. There's also the idea of a preemptive war, though in practice that is usually a pretext.