Updated September 21, 2021 at 12:25 PM ET

In a speech to the U.N. General Assembly on Tuesday, President Biden framed the U.S. withdrawal from Afghanistan as ending "a period of relentless war" and starting "a new era of relentless diplomacy."

Speaking to the delegates for the first time as president, Biden used the world stage to outline his administration's aspirations for cooperation with the nation's allies and called on nations to work together against COVID-19, climate change, human rights violations and "new threats" from emerging technology.

"We must work together as never before," he said.

Biden noted the deaths of some 4.5 million people worldwide from COVID-19, calling each death "an individual heartbreak."

"We need to act now to get shots in arms as fast as possible and expand access to oxygen, tests, treatments to save lives around the world," he said.

The U.S. is being criticized for authorizing booster shots when only small percentages of people in poorer countries have been vaccinated. Biden said the U.S. has spent more than $15 billion toward the global COVID-19 response and is committed to purchasing 500 million vaccine doses for use by the World Health Organization.

Biden also called for a new global health mechanism to "finance global health security" and a global health threat council to stay ahead of emerging pandemics.

Biden's approach is a departure from the Trump administration

Biden said the U.S. "will lead on all of the greatest challenges of our time, from COVID to climate, peace and security, human dignity and human rights, but we will not go it alone." The approach is a departure from that of the Trump administration, which embraced an "America first"-style of diplomacy that put nationalism ahead of multilateral efforts.

On climate, which Biden called a "borderless" crisis, the president said all nations need to bring "their highest possible ambitions" to the climate summit in Glasgow in November. He cited the new U.S. goal under the Paris Agreement set in April to reduce greenhouse gases to 50% below 2005 levels by 2030. Biden talked about investments he's working on with Congress, including for "green infrastructure and electric vehicles." Although, that agenda currently is in peril on Capitol Hill.

He declared that "government by and for the people is still the best way to deliver for all of our people," and while not mentioning China by name, he spoke of several challenges the U.S. sees with Beijing, including cyberattacks, protecting intellectual property and economic safeguards, freedom of navigation, and disinformation.

He said there is a need to avoid moving from "competition to conflict," then declared that the U.S. is "not seeking a new Cold War, or a world divided into rigid blocks."

However, he said the U.S. will oppose attempts by "stronger countries to dominate weaker ones."

On Iran, Biden said that the U.S. remains committed to keeping the Tehran government from developing nuclear weapons and said the U.S. is prepared to return to full compliance with the Iran nuclear deal if Iran does the same.

Biden's determination to strengthen the U.S. relationship with its traditional allies has been met with some skepticism in foreign capitals.

Last week, France recalled its ambassador to Washington following the surprise announcement from the U.S. and U.K. about sharing nuclear submarine technology with Australia, undercutting a $60 billion deal for diesel subs that France had with the Canberra government.

The U.N. secretary-general warns of a 'cascade' of crises

Before Biden spoke, U.N. Secretary-General António Guterres warned that "the world must wake up" given what he called "the greatest cascade of crises in our lifetimes."

"We are on the edge of an abyss — and moving in the wrong direction," Guterres said. "Our world has never been more threatened, or more divided."

Biden will keep his stay in New York brief because of COVID-19-related concerns. He met with Australian Prime Minister Scott Morrison there and plans to meet with U.K. Prime Minister Boris Johnson later Tuesday in Washington. In addition, there will be a virtual COVID-19 summit on Wednesday.

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