For some reason I just assumed that the war in Afghanistan was in fact approved by the UN Security Council. I don't know why I thought that, but it's false. Since the UN Charter is the supreme law of the land this means that the war was illegal even according to US laws. The UN Charter mandates that countries settle their conflicts peacefully and that force is not permissible unless authorized by the Security Council, except in the case where it is required to repel an imminent attack, which did not apply here.
Despite that did Congress pass a law authorizing the war? It would seem they did not. The Congressional authorization granted the President the authority to use force "against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons, in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons."
Did the Taliban do that? Nobody I know claims that they did. None of the 9-11 hijackers were Afghans. Two may possibly have passed through Afghanistan. That's about it. The Congressional authorization no more gives the President authority to attack Afghanistan than it gives him authority to attack Germany, where some of the planning is believed to have occurred.
What a ridiculous and destructive war. And Congress knows this stuff. It's not like they don't have Ron Paul on the floor informing them of the facts. Here he goes. At least we still have Ron Paul.