Afghanistan was perfectly legal

A recent post on Alternet alleged the illegality of the US war in Afghanistan.

"The invasion of Afghanistan was not legitimate self-defense under article 51 of the charter because the attacks on Sept. 11 were criminal attacks, not "armed attacks" by another country. Afghanistan did not attack the United States. In fact, 15 of the 19 hijackers came from Saudi Arabia. Furthermore, there was not an imminent threat of an armed attack on the United States after Sept. 11, or Bush would not have waited three weeks before initiating his October 2001 bombing campaign."

The fact that the 9/11 attacks were illegal under just in bello doesn't mean that they weren't armed attacks. The two phrases aren't mutually exclusive. The purpose of the requirement for an "armed attack" is to distinguish such actions from economic sanctions or other actions that don't involve deadly force.

The justification wasn't just 9/11. From its Afghan base, al-Qaida did the 1998 embassy attacks, the 2000 attack on the USS Cole and 9/11. In 1998, bin-Laden stated that it was the duty of Muslims to kill Americans wherever the opportunity existed. Thus, we were dealing with a sequence of armed attacks and the clear threat of more. The idea that someone can initiate an ongoing state of hostilities and that we need UN permission to respond as long as the attacks are spaced out is ridiculous. The idea of the need for an attack being imminent is to bar preventive war (the idea that a threat is building up but not imminent), not to require UN permission to deal with an aggressor who is spacing his attacks.

The Taliban not only failed to take action to stop this but also benefitted from the alliance. Specifically from whatever money bin-Laden could bring in and from the presence of his partisans on the front against the Northern Alliance. Afghanistan thus allied with, and provided a base of operations for, al-Qaida's attacks on the United States, giving us a casus belli against them.

Having said that, it is also true that the exception has swallowed the rule here. Dealing with al-Qaida in Afghanistan required military action. To label the entire struggle against Islamist militants as a "war", however, was clearly a propaganda ploy used to justify all manner of sins, including an unconstitutional use of executive power. For the most part, this is a matter of police and intelligence operations. The fact that Afghanistan is an exceptional case doesn't change that.

The post also made some spurious comparisons

Iranians could have made the same argument to attack the United States
after they overthrew the vicious Shah Reza Pahlavi in 1979 and he was given
safe haven in the United States. The people in Latin American countries
whose dictators were trained in torture techniques at the School of the
Americas could likewise have attacked the torture training facility in Fort
Benning, Ga.

The only problem with those comparions is that there is no indication that
the Shah was planning counterrevolutionary activities from his hospital
bed. Likewise, whatever was being taught at Fort Benning, the acts of the
students weren't launched from there.