President Barack Obama welcomed the leaders of 10 Southeast Asian nations on Monday for a two-day summit that marks an unprecedented bid to deepen U.S. ties to a distant region that barely registers in the consciousness of most Americans.

Obama's reasons may not be immediately obvious: The leaders who arrived here at the lush Sunnylands retreat represent relatively small countries, including some of the world's poorest, such as Laos and Burma. Many of them head corrupt regimes with dismal human rights records. And, in general, the United States has had difficulty promoting democracy in a region where Cambodian Prime Minister Hun Sen has ruled for 31 years and a military junta seized power in Thailand two years ago. Vietnam and Laos remain one-party states.

But against that turbulent backdrop, the Obama administration has sought to help shape the economic and strategic direction of the region because, knitted together, the countries boasts surprising clout. Known as the Association of Southeast Asian Nations, or ASEAN, the group cumulatively represents the world's seventh-largest economy; it is the United States' fourth-largest trading partner and has a population twice the size of the United States'.

READ: Prime Minister Najib Razak at US-ASEAN leaders summit hosted by Obama

The summit is the capstone of the administration's bid to help develop ASEAN into an institution capable of addressing the region's most pressing challenges - economic development, counterterrorism and climate change, to name a few.

National Security Adviser Susan Rice said the first-of-its-kind gathering "is a return on seven years of significant and sustained investment. It demonstrates our enduring commitment to this region."

Underpinning the effort is the White House's concern that without U.S. leadership, the diverse mix of nations will fail to coalesce around a common agenda and that some of them may be drawn closer to China, which also has sought to expand its influence in the region.

The engagement has included the installation of a full-time U.S. ambassador to ASEAN, based in Jakarta, Indonesia, and the president has made seven trips to the region, more than twice the number of any of his predecessors. This fall, Obama is scheduled to become the first U.S. president to visit Laos, and he is expected to make his first trip to Vietnam this spring. Rhodes, who ran a half-marathon in Luang Prabang last fall, and Secretary of State John Kerry took separate trips to Laos in recent months.

"Our strategy from the beginning was to move ASEAN's center of gravity toward greater cooperation with the U.S.," said Evan Medeiros, who served as Obama's senior Asia adviser from 2013-2015. Medeiros credited Obama with accomplishing that goal on many fronts, but he emphasized that the long-term challenge in Southeast Asia is that "their interests and ours are not perfectly aligned."

Obama extended the Sunnylands invitation to the group while attending a regional summit in Malaysia last November. During a town hall event in Kuala Lumpur, the president reminded his audience that he had lived in Indonesia with his mother and stepfather as a young boy.

"This is part of who I am," he said, "and how I see the world."

The question is whether he can persuade others to see it the same way.

The centerpiece of Obama's engagement in Asia is the 12-nation Trans-Pacific Partnership trade accord, which includes four ASEAN countries. But the deal, formally signed this month, has not been ratified by the U.S. Congress and remains in limbo.

Historic democratic elections in Burma, supported by the White House, resulted in a transition of power to the long-oppressed opposition party last fall, but the leadership turnover remains fragile. Outgoing president Thein Sein has elected to skip the Sunnylands gathering, and opposition leader Aung San Suu Kyi is still locked in talks with military regime and will not attend either.

Renewed partnerships with the Philippines have bolstered U.S. naval presence in the region in the face of aggressive maneuvers by China in the South China Sea. But closer political ties to Malaysia - Obama played golf with Prime Minister Najib Razak in Hawaii in 2014 - have been frayed by allegations that Najib embezzled hundreds of millions of dollars and that subsequently his administration cracked down on political dissent.

Obama aides said they always recognized that progress in a region long neglected by the United States would be fitful and uneven.

In remarks welcoming the leaders, Obama said that the United States intends to play a "long-term role" that is "central to the region's peace and prosperity and to our shared goal of building a regional order where all nations play by the same rules."

The leaders are focusing on common interests at Sunnylands, where the agenda includes maritime security in the South China Sea, trade ties and counterterrorism. The Islamic State terror group claimed responsibility for a series of attacks in Jakarta last month that killed seven people and injured 23, and White House officials said they fear the militant group is seeking a foothold in the region.

Climate change and the environment - including devastating forest fires in Indonesia that have been cited among the world's worst environmental disasters - also will be discussed, officials said.

China is on the agenda, as well. Ernest Bower, a Southeast Asia expert at the Center for Strategic and International Studies, said the White House aims to enlist the Southeast Asian nations as a bulwark against China's ambitions.

"That's code for, 'We've got to convince China to play by the rules,' " Bower said.

Although Beijing is investing large sums of money and capital to create a new "silk road" of prosperity - including its own regional trade pact - China has intimidated its neighbors through its aggressive expansion, White House aides said.

China's construction of man-made islands in the South China Sea, potentially for military use, has alarmed several countries, especially Vietnam, that have long-standing claims in one of the world's busiest shipping corridors. Hanoi has signaled a new openness to engage with the West, and the Communist Party general secretary visited the White House for the first time last summer.

Even the setting at Sunnylands, a retreat once favored by presidents Richard Nixon, Ronald Reagan and George H.W. Bush, is intended to send a message to Beijing.

The first time Obama held a summit there was in 2013 for Chinese President Xi Jinping. Obama's return for the ASEAN summit has been viewed in some quarters as "poking a stick at China," said James Keith, the U.S. ambassador to Malaysia from 2007-2010.

The Southeast Asian nations are reluctant to choose sides, wary about being used as pawns in a geopolitical struggle between superpowers. The risk, Keith said, is making the leaders think that "we're mostly interested in you as a means to an end - and that is messaging China."