One of the main conclusions arising from the new US national security strategy under President Obama is that he has modified the Bush doctrine of pre-emption.
Pre-emption was the defining aspect of President Bush's approach to foreign policy, one prompted by the attacks of 9/11 and one which culminated in the invasion of Iraq in 2003.
President Obama has stepped back.
You can see this in the difference in wording between the document just issued and the one from President Bush in 2006. US presidents are required by Congress to produce these documents of doctrine every four years.
In 2006, George Bush's doctrine said: " We do not rule out the use of force before attacks occur... We cannot afford to stand idly by... This is the principle and logic of pre-emption."
In 2010, President Obama, in a specific paragraph called "Use of Force" says: "While the use of force is sometimes necessary, we will exhaust other options before war whenever we can... when force is necessary we will continue to do so in a way that reflects our values and strengthens our legitimacy..."
This last, rather tortuous phrase, means that the US will seek international legitimacy (through the UN or Nato, it says) before acting. However, as any American president would, Mr Obama maintains an option to go it alone: "The US must reserve the right to act unilaterally if necessary."
His refusal to rule out unilateral action has led some to doubt that there is a new doctrine at work here. Foreign Policy magazine says: "The reality is that the new strategy is best characterised as 'Bush Lite', a slightly watered down but basically plausible remake..."
However, the thrust and spirit of the two documents is quite different. George Bush refers to the "War on Terror" and Barack Obama does not. While neither blames Islam for al-Qaeda, one comes close by referring to the "perversion of a proud religion", the other simply has "a far-reaching network of violence and hatred".
Iran is another example. The Bush version made an implicit threat of force if Iran defied the UN, saying: "This diplomatic effort must succeed if confrontation is to be avoided."
The Obama version is that the US will "work to prevent Iran from developing a nuclear weapon" (even though Iran says it is not doing this and note that the commitment is only to working to prevent, not actually preventing) and that "multiple means" will be employed to this end. "Multiple means" does not rule out force but is some way from threatening it.
Both say that America will "lead" but their leadership is of a different order. The Bush document talks ambitiously about the "ultimate goal of ending tyranny" in the world through the spread of democracy. The Obama one is more modest: "The burden of a young century cannot fall on America's shoulders alone."
And in two key comments the Obama document states: "In the past we have had the foresight to... avoid acting alone".
And: "America has not succeeded by stepping outside the currents of international co-operation."
There has therefore been a toning down of US ambitions and the means by which they should be achieved. President Obama also lays much more stress on getting things right at home.
There is no surprise here. The character of the president will determine American foreign policy. President Obama is different from President Bush. We knew that, from words and deeds. This national security strategy simply confirms it.
This does not mean that President Obama will not fight wars. He is already fighting in Afghanistan. Many American presidents who dislike armed conflict have it thrust upon them - Jimmy Carter felt he had to try to rescue the hostages in Tehran by force, Bill Clinton bombed al-Qaeda camps.
What this document does is to try to lay out the framework under which such actions will be taken.