Since the fall of the Soviet Union, what nations have come looking for a fight with the United States? The only attacks on US soldiers and civilians were carried out by terrorist organizations, not by any of the nations we've gone to war with.
The only legitimate defensive war we've had in the last 30+ years has been Afghanistan, where the Taliban were backing Al Quaeda (of course, the Saudi clerics who funneled Saudi oil money to both the Taliban and Al Quaeda remained unpunished).
Libya and Quaddafi would have been legitimate targets...28 years ago, when he was funding the terrorists who brought down Pan Am 103, not in 2011, when Quaddafi was working with US intelligence to get rid of Al Quaeda cells in Libya.
As for the rest, I don't recall Serbia ever attacking the US or any US interests or allies, unless you believe Bosniak and Kosovar Muslims are honorary US citizens. Nor did Saddam Hussein's Iraq have anything to do with 9/11, he was a red herring used by the Bush administration to protect Bush's friends in Saudi Arabia. The same applies to Assad in Syria - how did Al Nusra Sunni rebels come to be seen as honorary US citizens in need of our protection?
Terrorist organizations always have the backing of some government or other. Iran has been the longest at it, even openly. Red China, North Korea and Russia have been the biggest friends of Iran, with the European Union (under Germany’s de facto leadership) close behind.
The only attacks on US soldiers and civilians were carried out by terrorist organizations