osama was responsible for only 1 war. where the usa is responsible for many more.
USA government after 1945 till now.
okay, let's look at the biggest wars:
Korea: justified. They helped defending South Korea from the Communist North Korea.
Vietnam: I'm not sure. There are pro and cons. I also don't really know much about it, maybe someone can enlighten me. But most people will probably say that it wasn't justified.
First Gulf War: justified. It was the answer to Iraq's invasion of Kuwait.
Yugoslavia: justified. They prevented a genocide.
Afghanistan: justified (at least I think so). They fought the Talibans.
Second Gulf War: justifed in my opinion. Saddam was a genocidal dictator.