Presidents, prime ministers and diplomats will take on a variety of global challenges at the United Nations this week, from halting the advance of a devastating disease to eliminating the specter of attacks from a formidable architect of terrorism.
UN Secretary-General Ban Ki-moon said the weeklong annual General Assembly is among the most pressing in recent years, as global military and humanitarian quagmires mount apace.
Also to be addressed is the civil war in Syria, now 3 1/2 years old, civil strife in South Sudan, the shattered relationship between Israelis and Palestinians after the war in Gaza and simmering tensions over military clashes in Ukraine.
"I am convinced that this 69th session of the General Assembly could be the most consequential in a generation -- and for a generation," Ban said as he opened the gathering in Manhattan, welcoming up to 140 heads of government and state.
"The coming year must be a time for action; a time for results. We have important tests before us, and high expectations across the range of peace, development and human rights challenges," he said.
President Barack Obama, who will spend three days at UN events, will be among the busiest government leaders. Last year, he spent one day at the UN.
Tuesday, Obama will attend Ban's high-level climate change summit, an ambitious effort encouraging world leaders to address the problem of rising seas, melting ice caps, deforestation and fossil fuel emissions. Also Tuesday, the president will attend the annual meeting of the Clinton Global Initiative.
In addition, Obama will chair a summit to tackle the increasing threat of the Islamic State, a rising Mideast terror group deemed a global threat. The group captured large swaths of Iraqi territory this summer after waging war against Syria's president, Bashar Assad, and it has recently claimed responsibility for beheading Westerners in revenge for U.S. airstrikes.
Obama will speak before the world body's 192 other member states and observers on Wednesday at the General Debate and at a special session of the UN Security Council to make the case for a resolution that would require member states to ban people from traveling to war zones to join extremist groups.
The measure comes on the heels of authorization Obama received from Congress to deal with the Islamic State by training and equipping Syrian rebels to fight the group -- and as reports surface of Westerners seeking to join the extremists.
The spread of Ebola, a disease that has claimed more than 2,600 lives in West Africa, will also take center stage at the General Assembly, just days after the Security Council approved an unprecedented resolution to bring resources to bear to tackle the problem.
Obama, who recently authorized sending up to 3,000 U.S. military personnel to Africa to fight the outbreak, will attend a UN meeting Thursday to discuss the global response to Ebola.
Ban stressed that member nations must not lose sight of traditional topics addressed by the UN, including poverty, illiteracy, and inadequate sanitation and health care.
"This General Assembly stands as the ultimate rebuke to that distorted and venomous view of the world," he said. "Here we stand -- nations united -- to demonstrate that in our interconnected, ever-smaller interdependent world, the best way to solve problems is by working together in a more determined way than ever before."