By Paul Reynolds
World affairs correspondent, BBC News website
President Obama signalled a shift in the US approach to the international stage
Slowly the shape of the world after the financial flood is beginning to emerge.
The first thing to be said is that everyone is in the same boat. And they have to bail together. This contrasts to the old days when capitalists and communists exchanged insults as their ships passed in the night.
The worst threat at this G20 summit was a remark by French President Nicolas Sarkozy that he would walk out if there was not better regulation of banks and financial markets, not exactly the kind of casus belli that plunged Europe into war nearly 100 years ago. We have moved on. Nor did he walk out. Indeed, he was pleased, he said, at the result.
The Franco-German analysis might well have been right. But being right about the past does not mean that you alone can put right the future. The European Union as a whole, normally so free in its advice to all and sundry, was a bit chastened, with many newer and some older members on the verge of or in financial crisis.
We have moved on too from the 1930s, when depression helped fuel the rise of dictatorships. Whether the world solves its financial crisis this time has yet to be determined, but the players at least seem to have learned some lessons.
Stronger relationships mean better chances of dealing with problems
The second thing is that the position of the United States has changed.
President Obama came and conquered, with little gestures like shaking hands with a black policeman guarding 10 Downing Street to the larger "listen and lead" attitude he showed at the conference itself.
There was no longer the sense of American particularity that there was under George W Bush.
President Obama spoke of an "era of responsibility" - meaning no more wild financial dealings and a willingness to take joint corrective action with others.
He accepted that America could not solve the crisis by itself (though its critics would say that it managed to cause it largely by itself). This was a return to multilateralism - and a recognition that American ways were not necessarily the best ways.
It extended beyond economics. Mr Obama had a productive meeting with Russian President Dmitry Medvedev at which they agreed to start negotiations on new nuclear weapons reductions and complete them by December.
They managed not to allow their differences - over missile defence or Georgia to name but two - to prevent the reset button from being pressed.
This does not mean that all will be well in their relationship. But it does mean that there are better prospects for overcoming problems.
Leaders of less developed countries such as Brazil can no longer be ignored
Then there was China. Chinese President Hu Jintao did not make much of a public impact, beyond that in his own media, but China's influence was felt everywhere. They and the Americans agreed on a "strategic and economic dialogue" to start in Washington this summer.
The workshop of the modern world cannot be ignored. One sign is that China is likely to get much larger voting rights in the IMF to match its much larger contributions.
Can the day be long delayed when China enters the trading world fully, with a convertible currency?
This is the new super power diplomacy - not East versus West, nor a return to the disastrous manoeuvring of the late 19th Century or the 1930s, but the management of relationships within better agreed rules.
And do not forget the presence of leaders from places like India and Brazil. They cannot be ignored either.
It makes one wonder how much longer the old G8 style of meeting, another of which is planned in Italy this summer, can stagger on.
There can be no rich man's club if the members are no longer so rich and have caused so much disaster.