G20 leaders gathered Sunday in South Africa hailed multilateralism -- even as they struggled to adapt to a changing world order beset by go-it-alone US policies, wars and deepening geopolitical rivalries.

The final day of their weekend summit -- boycotted by the United States -- kicked off with a searching discussion on how the G20 can survive in a fragmenting world.

"We are not experiencing a transition, but a rupture," acknowledged Canadian Prime Minister Mark Carney to journalists just before the summit session.

"Too many countries are retreating into geopolitical blocs or the battlegrounds of protectionism," he said, but added: "In every rupture resides the responsibility to build -- nostalgia is not a strategy."

Dozens of leaders from key economies around the world -- including Eu

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