President Obama seems to have dramatically revised US nuclear strategy by renouncing the first use of nuclear weapons. He also said the United States will never use nuclear weapons against non-nuclear states. But has American nuclear strategy really changed fundamentally?

On the face of it the change in policy is substantial. But there are elements of the traditional US "carrot and stick" approach in the new policy. The declaration presents Iran with a clear choice: Only if it opens up its nuclear program to international inspection will it receive assurances it will not be subject to a nuclear first strike.

Since there is almost zero possibility of a nuclear war among the big powers as the result of such a war would be mutual destruction, the U.S. sees the main threat coming from Iran and terrorist organizations. America reckons Iran will be a greater threat if it develops nuclear capability, and the new US policy is addressed squarely to what it regards as a "rogue state".

Obama's declaration was billed as wholly new nuclear doctrine for the future. But its underlying motives lie deeper. US global strategy has evolved as a result of the 9-11 attacks. Washington no longer sees the main threat coming from traditional rivals like Russia and China. Relations with such traditional powers can be managed by treaties and dialogue. Institutionalization of these relationships seems to be the direction of US foreign policy, albeit an institutionalization based on a thoroughly realist assessment of US national interests.

Although the United States, Iran and terrorist organizations are asymmetric in terms of both hard and soft power, a definite strategy is still needed to ensure US security. The U.S. has so far been wielding the stick – applying sanctions. But the recent declaration includes a carrot. It will take time to see if the carrot modifies Iran's behavior. For the foreseeable future this is unlikely. Even though the U.S. wants to promote the institutionalization of international politics, the reality is that neo-realism – or the law of the jungle – still prevails, and each state puts its own national interests first.

President Obama's new declaration is also based on US national interests. So US nuclear doctrine has changed less than many believe, but a small change is better than no change at all.

The author is Ph.D candidate of International Politics, School of International Relations and Public Affairs, Fudan University.