The United Nations General Assembly convenes on Tuesday in the shadow of the second year of war in Ukraine, amid a series of climate related catastrophes and at a time of increasing divisions in the world that will hamper efforts to address the litany of problems contributing to the strains.

Underscoring the tensions, only President Joe Biden among the leaders of the five nations of the Security Council — the United States, Russia, China, France and Britain — will attend the meeting. Ukraine’s president, Volodymyr Zelensky, will be there in person for the first time since Russia invaded his country, though Ukraine is not dominating the agenda as it did last year.

This year’s gathering was planned with an eye to growing demands from the nations of the “global south,” an informal group of developing and underdeveloped countries. They have been frustrated by the world’s attention on the conflict in Ukraine while their crises have received minimal attention and funding, diplomats said.

Responding to those demands, the U.N. has scheduled discussions during the General Assembly on climate change, sovereign debt relief and ways to help struggling countries reach the U.N.’s development goals on prosperity, health, development, education and gender equality.

“We will be gathering at a time when humanity faces huge challenges, from the worsening climate emergency to escalating conflicts, the global cost-of-living crisis, soaring inequalities and dramatic technological disruptions,” António Guterres, the secretary general of the U.N., said in a briefing for reporters last week. “People are looking to their leaders for a way out of this mess.”

Mr. Guterres acknowledged, however, that it was becoming increasingly difficult to bring U.N. member states together, given the depth of the divisions that were revealed by the absence of world leaders at the forum.

President Vladimir V. Putin of Russia and President Xi Jinping of China will sit out the event for the second year in a row. But more surprising were the absences of President Emmanuel Macron of France, the British prime minister, Rishi Sunak, and India’s prime minister, Narendra Modi.

“It’s important that countries participate in this forum, it happens only once a year,” said Linda Thomas-Greenfield, the United States ambassador to the U.N. when asked at a news conference on Friday if she was disappointed that not only America’s rivals but also its allies were skipping the event this year. Ms. Thomas-Greenfield added that President Biden plans to reinforce the theme that “multilateralism is back.”

France’s mission to the U.N. said that Mr. Macron had a scheduling conflict, hosting Britain’s King Charles III in Paris this week. Britain did not provide a clear answer for why Mr. Sunak was missing his first General Assembly. Both countries will be represented by a delegation of ministers.

Analysts said that world leaders skipping the U.N. risked weakening the institution at a time when it was already struggling to remain relevant. The U.N.’s various agencies are still at the forefront of organizing and providing humanitarian aid. But as the war in Ukraine has raged and a head spinning series of military coups have overthrown governments from coast to coast in Africa, the U.N’s role as a negotiator and mediator has been marginalized for the most part.

The Security Council, which was designed to be a major force in maintaining peace and stability, has been notably absent in efforts to resolve these issues, paralyzed by divisions among its veto-holding members.

“The situation at the U.N. is now bleak,” said Richard Gowan, the U.N. director for the International Crisis Group, a conflict preventing organization. “We are a lot closer to a cliff edge in U.N. diplomacy, and major power tensions are having a more and more serious effect on the organization.”

Tensions between the Western world and the global south was a major factor in the planning for the General Assembly this year, diplomats said. The United States and European allies have grown weary, they say, of Russia and China luring these countries out of the Western orbit and are determined to strengthen relations with the developing world.

“If it were up to us we would spend more time discussing Ukraine,” said Olof Skoog, the European Union’s ambassador to the U.N.. But he said the aim this year was to prevent the north-south rift from deepening and to pay attention “to the fact that for the developing world, this week the central element is about development.”

Ukraine is still on the schedule. The Security Council will hold a session on the war on Wednesday that could present theatrical moments, with Mr. Zelensky possibly sitting at the same table with Russia’s foreign minister, Sergey V. Lavrov — provided that both men remain in their seats as the other speaks. Secretary of State Antony J. Blinken will also be present.

Mr. Zelensky is expected to try to persuade fence-sitting countries to rally behind Kyiv’s war effort. He is also expected to rebut the growing chorus, emerging among some conservatives in the United States as well as within some global south countries, calling for immediate peace talks on ending the war.

Those calls have been echoed by Mr. Guterres, who has repeatedly said the conflict must end, but with Russia respecting the U.N. charter and international law. That would mean withdrawing all its forces from Ukraine, experts have said, but Mr. Guterres has carefully refrained from saying that publicly.

As he said in the briefing for reporters last week, “Politics is compromise. Diplomacy is compromise. Effective leadership is compromise.”