The history of warfare shows that aggressor countries always feel impelled to
attack,often for reasons that seem irrational to outsiders. Imperial Japan felt that its need for access to natural resources justified the invasion of Manchuria. Imperial Germany's militaristic mentality hoped to advance Germany's standing in the world through European conquest.

In the case of the Iraq war, the Bush administration regarded the rule of Saddam Hussein and his sons as a permanent strategic threat. This threat was not perceived to be immediate,despite the weapons of mass destruction propaganda. Instead,the administration feared what Saddam would do with massive oil revenues should he behave himself long enough to get the UN sanctions lifted. Chances are Saddam would have attempted to acquire nuclear weapons.

In international relations,war can't be justified on the basis of possible future threats,but that didn't stop the Bush administration.

It now faces a possibly similar threat from Iran. Should Iran acquire nuclear weapons, that would change the balance of power in the world and in the Middle East,leading to nuclear arms races. It wouldn't take more than a dozen Hiroshima size atom bombs to serve as an effective nuclear deterrent to America,which could not risk the destruction of any of its major cities.

That's why any attempt by Iran to develop nuclear weapons would lead to a war with America.

Will the Iranian government try to acquire them? This clerical government
is still inspired by the principles of the Iranian revolution and revolutionaries are almost always unpredictable and truculent. It will be a close call.