Speaking to the annual Munich Security Conference virtually, Biden ticked through a daunting to-do list — salvaging the Iran nuclear deal, meeting economic and security challenges posed by China and Russia and repairing the damage caused by the coronavirus pandemic — that he said would require close cooperation between the U.S. and its Western allies.

Without mentioning Donald Trump's name once in his speech, Biden mixed talk of a reinvigorated democratic alliance with a rebuke of his predecessor's approach, a message warmly received by Western allies.

''I know the past few years have strained and tested the transatlantic relationship,” Biden said. “The United States is determined to reengage with Europe, to consult with you, to earn back our position of trusted leadership.”The president also participated Friday in a virtual meeting of the Group of Seven industrialized nations, where leaders managed to work Biden's campaign theme into their closing joint statement, vowing to “work together to beat COVID-19 and build back better.”“Welcome back, America,” said European Council President Charles Michel, effectively summing up the mood of the Munich conference.

But while such happy talk conveyed the palpable sense of relief among allies at Biden's full-throated commitment to mending frayed U.S.-Europe relations, plenty has changed over the past four years in ways creating new challenges.

China has cemented its place as a fierce economic competitor on the continent as the U.S. has reconsidered long-held national security and economic priorities embedded in the transatlantic alliance. Populism has grown through much of Europe. And other Western countries have, at moments, sought to fill the vacuum left as America stepped back from the world stage.

German Chancellor Angela Merkel noted that some differences between the U.S. and Europe remain “complicated.” Europe sees China's economic ambitions as less of an existential threat than the U.S. does and has its own strategic and economic concerns that are not always in sync with Biden on Russia as well.

Still, Merkel, who had a strained relationship with Trump, didn't hide her preference for an American foreign policy informed by Biden's world view.

“Things are looking a great deal better for multilateralism this year than two years ago, and that has a lot to with Joe Biden having become the president of the United States of America,” Merkel said.

“His speech just now, but also his administration's first announcements, have convinced us that this is not just talk but action.”Biden made his address to a global audience as his administration this week took steps to reverse key Trump administration policies.

He said that the U.S. stands ready to rejoin talks about reentering the 2015 multilateral Iran nuclear deal abandoned by the Trump administration. The Biden administration announced Thursday its desire to reengage Iran, and it took action at the United Nations aimed at restoring policy to what it was before Trump withdrew from the deal in 2018.

Biden also spoke out about the two-decade war in Afghanistan, where he faces a May 1 deadline to remove the remaining 2,500 U.S. troops under a Trump administration negotiated peace agreement with the Taliban. He also called for cooperation in addressing economic and national security challenges posed by Russia and China and identified cyberspace, artificial intelligence and biotechnology as areas of growing competition.

“We must prepare together for long-term strategic competition with China,” Biden declared.

His message was girded by an underlying argument that democracies -- not autocracies -- are models of governance that can best meet the challenges of the moment. The president urged fellow world leaders to show together that “democracies can still deliver.”At the G-7, administration officials said, Biden focused on what lies ahead for the international community as it tries to extinguish the public health and economic crises created by the coronavirus pandemic. He announced the U.S. will soon begin releasing $4 billion for an international effort to bolster the purchase and distribution of vaccine to poor nations, a program that Trump refused to support.

Biden's turn on the world stage came as the U.S. officially rejoined the Paris climate agreement, the largest international effort to curb global warming. Trump announced in June 2017 that he was pulling the U.S. out of the landmark accord, arguing that the pact would undermine the American economy.

Biden announced the U.S. intention of rejoining on the first day of his presidency, but he had to wait 30 days for the move to go into effect. He has said that he will bake considerations about climate change into every major domestic and foreign policy decision his administration faces.

"This is a global existential crisis," Biden said.

Biden also encouraged G-7 partners to make good on their pledges to COVAX, an initiative by the World Health Organization to improve access to vaccines, even as he reopens the U.S. spigot.