WASHINGTON -- It was supposed to be his grand valedictory tour. Now President Barack Obama must use his last major trip abroad to try to calm shocked world leaders about the outcome of the U.S. election, and what comes next when Donald Trump is president.

Trump's unforeseen victory has triggered pangs of uncertainty at home and grave concerns around the world.

Obama departs Monday and stops first in Athens, where he'll tour the Parthenon, meet with the prime minister, and give a speech about democracy and globalization.

He'll use his visit to Berlin to show gratitude to German Chancellor Angela Merkel and to meet with key European leaders.

In Peru, he'll attend a major Asian economic summit in Lima, and also meet with the leaders of China and Australia.