 Because Article 5 says, in essence, an attack on one is an attack on all. We'd be allowing a member that was involved in a conflict to join us, and therefore we'd have to be their steadfast allies. For example, of course, Article 5 was invoked by the NATO allies when the United States was attacked on September 11, 2001. And second, as we saw with the admission of both Finland and Sweden, admission of a new member requires consensus, as does all major decisions by the alliance. All alliance members have to support that decision.