U.S. President Donald Trump's return to the White House has been met with both relief and disappointment across world markets as investors try to work out what the next four years will bring.

World leaders congratulated President Donald Trump on his inauguration Monday, with many urging stronger alliances or continued cooperation between their countries and the United States, in carefully crafted social media posts and statements.

The dollar weakened ahead of the inauguration, as the Trump administration signaled that new tariffs would not be imposed on the new president's first day in office. Start the day smarter. Get all the news you need in your inbox each morning.