In his first address to the United Nations, US President Joe Biden has pledged cooperation with allies through "a decisive decade for our world".
His reassurances come amid tensions with allies over the US' Afghanistan withdrawal and a major diplomatic row with France over a submarine deal.
Mr Biden campaigned on returning America to a global leadership role, which he reaffirmed on Tuesday.
"I believe we must work together like never before," said the president. The 76th General Assembly in New York City takes place against the backdrop of a climate crisis and a once-in-a-century pandemic, both of which have sharpened global divides.
Mr Biden pushed for cooperation on these fronts, saying: "Our own success is bound up in others succeeding as well."
Amid ongoing tensions between the US and China, Mr Biden stressed that the US is "not seeking a new Cold War or a world divided".
But he said the US would vigorously "defend ourselves, our allies and our interests against attack".
He also touted his pullout from Afghanistan, which has been criticised by allies at home and abroad, and added that "military power must be our last resort".
World leaders at odds with former President Donald Trump had hoped for a more stable and reliable America under his successor's leadership - but Mr Biden's most recent foreign policy moves have made some uneasy.
The US' lack of coordination during the Afghanistan exit after two decades of war rankled allies and led to an international scramble to evacuate. The Nato mission at the time of the withdrawal comprised troops from 36 countries, three-quarters of whom were non-American.
Last week, a trilateral US-UK deal to provide Australia with nuclear-powered submarines infuriated the French, who had their own five-year-old contract to build conventional submarines for the Australians.
French foreign minister Jean-Yves Le Drian described the agreement as "a stab in the back", and the top French diplomats in both countries were recalled.
The Biden administration has also seen international criticism over alleged US hoarding of Covid-19 vaccines and non-reciprocal travel restrictions.