There was a recurring rhythm to President Barack Obama's speech about the no-fly zone over Libya. But it wasn't a drum beat of war - it was a chorus about consensus, an insistence on internationalism.

Sure, there was an ultimatum, the threat of military action. Those are the headlines. And there was an explanation why America might have to fight.

Left unchecked, we have every reason to believe that Gaddafi would commit atrocities against his people. Many thousands could die. A humanitarian crisis would ensue. The entire region could be destabilised, endangering many of our allies and partners. The calls of the Libyan people for help would go unanswered. The democratic values that we stand for would be overrun. Moreover, the words of the international community would be rendered hollow.

But the subtext is more important. Read the last sentence in that quotation again. In a speech of just over three pages he repeats this point. Not once:

The US has worked with our allies and partners to shape a strong international response.

Not twice:

The US is prepared to act as part of an international coalition. American leadership is essential, but that does not mean acting alone.

Not three times:

It is not an action that we will pursue alone. Indeed, our British and French allies, and members of the Arab League, have already committed to take a leadership role.

But more:

So I have taken this decision with the confidence that action is necessary, and that we will not be acting alone.

So you might have gathered, the US is not going it alone. Throughout his declaration Mr Obama makes it clear how different this is to the Iraq war. Not only the international consensus, but the limits on action.

I also want to be clear about what we will not be doing. The US is not going to deploy ground troops into Libya. And we are not going to use force to go beyond a well-defined goal -- specifically, the protection of civilians in Libya.

The limits he sets out are not just practical, they are limits to ambitions and objectives.

I want to be clear: The change in the region will not and cannot be imposed by the US or any foreign power; ultimately, it will be driven by the people of the Arab World. It is their right and their responsibility to determine their own destiny.

Mr Obama is only a reluctant convert to action, and you could argue he's merely disguising his feet-dragging with noble rhetoric about the international community. It's certainly noticeable that he didn't mention the killings in Yemen (although he earlier issued a statement condemning them) or the unrest in Bahrain, stiffer tests of American power and resolve.

But I think we are seeing something new. He is using a crisis thrust upon him to set out an Obama doctrine of sorts, to make a statement about America's relationship with the world. While he is in charge, he is saying, America will not go it alone, will set limits on what it does, and won't impose its will. Some will not like this,

and the world will find it difficult to adapt to a president who almost seems determined to lead from behind.

The Obama doctrine is a tightrope walk: Acting, but within limits, leading only as a first among equals.