Kijun Times

But the G20 record on global economic goals since has been much more mixed.

"When Obama came in, he made a big a difference, he had new ideas, and he wanted to show at home and internationally that the U.S. can drive the economic recovery," said Paola Subacchi, International Economics research director at foreign affairs think tank Chatham House.

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Obama came to the London summit with a clear message. To save the world from spiraling deeper into recession after the global financial crisis, the world's biggest economies must work together rather than isolate themselves.

"The G20 summit in London was a success, there was a big danger that countries would turn to protectionism to deal with the crisis, and Obama was very much against that," Subacchi said.

The summit was only the second gathering of the leaders of the world's 20 biggest economies in history. The inaugural meeting was hosted by the outgoing President George W. Bush in the fall of 2008.

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There have been G20 summits every year since then. But none have lived up to the 2009 meeting.

Financial markets, usually first to react to any sign of policy change, seem little bothered about the summits.

Analysis by the European Central Bank in 2014 found that the big G20 meetings have had at best "a mild calming impact on market developments" even at the height of the global financial crisis.

Clara Brandi, an economist at the German Development Institute, said the original G20 commitment not to erect new trade barriers was followed by little concrete action from the member countries.

"The summit declarations contain only vaguely drafted commitments to strengthen the multilateral trading system... the G20 should assume a more proactive role," she wrote in a note ahead of the China summit.

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As the worst of the financial crisis passed, so did the importance of the annual gatherings. And the forum has become fragmented as the conflict in Ukraine opened up deep divisions between the West and Russia and tensions rose over territorial disputes in the South China Sea.

At the same time, challenges posed by Europe's refugee crisis, the conflict in Ukraine or Brexit are more likely to demand regional rather than global solutions.

"The G20 has lost a lot of shine, because it's more about plumbing than about fixing the front of the building...but that's where the attention is," Subacchi added.

The serious business now takes place on the sidelines in informal meetings. The G20 provides a rare opportunity for leaders to meet -- such as the famous "power huddle" between Obama and Russian President Vladimir Putin during a break at the 2015 summit in Turkey.