I'm Unclear on Something

I'm puzzled about the concept of Iran's coming "pause" in nuclear development.

I know Iran is supposed to want nuclear weapons to prevent us from invading Iran (but isn't that why we have the anti-war movement?). That's the dictator's lesson from Iraq and Libya, right?

But if Iran signs a deal that delays their nuclear status 10-15 years, isn't Iran just giving us a decade to prepare a really devastating invasion?

So why would a fearful Iran sign a deal that keeps them vulnerable to invasion for ten years or more?