Van posted: Article 5 of the NATO treaty states that if any member is attacked, all the NATO members will individually and collectively counter-attack. Failure by any NATO member (except France, 'cause they're special and have an exemption) to counter-attack the AQ base in Afghanistan after 9-11 was a violation of the treaty.
I mean no offence, Van, but your comment invokes an all too common misperception that I feel compelled to rectify. I am being overly pedantic here, but Art 5 does not require that, if invoked, all NATO members are legally required to use military force (or counterattack, as you say). What Art 5 says is, to quote (italics added);

The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, ….. will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.
(Excerpted from Art 5 of The Washington Treaty 4 April 1949)
Simply put, a member state ‘could deem necessary only sending a get well card and sending the card would legally fulfill its Treaty obligations’ (this quote is from a NATO legal officer – so thanks to the LtCol for allowing me to use it). This ‘get out’ phrasing, so I have been given to understand, was used to facilitate the Truman Admin convincing the Senate to agree to the Treaty back in 1949 – so it was originally intended as a ‘get out’ for the US rather than for the Europeans. Of course, in ’49 the expectation was of Soviet aggression against NATO’s European member, not a direct attack against the US itself.

Much more important, however, in defence of the Europeans, many of them were willing to send combat forces to fight in Afghanistan in 2001 under Art 5. As one example, the Schroeder gov’t went to the Bundestag (due to German constitution requirements relating to sending German forces abroad) where it pushed through a successful vote, which if it had lost would have been a ‘vote of no confidence’ for Schroeder (and the vote barely passed), to send German combat forces (around 2000 in number, IIRC) to fight in Afghanistan with the US and NATO. The response of the Bush Admin was ‘Don’t call us, we will call you’ –and we all know the Bush Admin did not call. The Italians had a similar experience and the French were eager to be involved (they eventually were allowed send air forces and did [were allowed to?] drop ‘a’ bomb somewhere in the vicinity of Mazar-i-sharif in the north).

Simply put, the Bush admin decided to operate in Afghanistan with a ‘coalition of the willing’ rather than through NATO under Art 5 (which would have made it a NATO rather than US led operation) – and most European militaries were not invited to participate except in supporting roles (if that).

So, that NATO’s European members did not contribute combat forces was not a violation of the Treaty, primarily because the Bush admin decided in essence not to accept the help many of them offered under the invocation of Art 5 with respect to combat operations in Afghanistan (NATO did, for example, furnish a range of supporting activities, such as sending 5 of its AWACs to the US to provide air protection in 2001, to free up US AWACs for Central Asia). Worth noting in passing, I suppose, is that current NATO led ops in Afghanistan have not been authorized by the alliance under the aegis of the Art 5 invocation of 2001.

I’ll get off my hobby horse now. My deep apologies to all for being pedantic, way off topic.