When the top leaders of the United States, Japan, India and Australia met at a virtual summit on Friday, there was a clear message beneath the official statements: A new grouping of like-minded nations has arrived on the international stage.

It was the first meeting of the top leaders of the four participant countries in the loose coalition known as the “Quad,” and a significant step toward cementing a partnership of democracies — and counterweight to China — that had once appeared more concept than reality.

President Biden is building on the previous administration’s efforts to solidify the strategic partnership as he formulates his approach to China. Biden’s push for the first-ever meeting of leaders so early in the administration signals that the Quad will become a central part of the U.S. strategy in Asia, experts say.

“One thing it says is that this is certainly bipartisan. Both the concept of the Quad, as well as the [concept] that the Indo-Pacific region should be thought of as a grouping, have cut across partisan lines,” said Sameer Lalwani, expert at the Stimson Center who has studied the emerging coalition. “It’s an important signal that the Biden administration is pushing forward on this.”

Each of the countries has a complicated relationship with China, and the Quad is not a formal alliance. The countries do not explicitly call out what they view as Chinese aggression with one voice, and instead emphasize their desire to pursue a “positive vision” for the region.

Still, China remains the subtext of the Quad meetings. Building on the quartet’s partnership will be crucial to Biden’s strategy to remain tough on China, experts say.

“The underlying message is that they have the willingness and resolve that they should work together on China, even if they don’t mention China in their respective statements,” said Derek Grossman, senior defense analyst at the Rand Corp.

Until now, the Quad has consisted of meetings of senior officials, as well as a joint naval exercise last November.

On Friday, the four nations pledged to jointly manufacture and deliver up to 1 billion doses of coronavirus vaccine throughout Southeast Asia and potentially elsewhere by the end of next year. The vaccine would be produced by India, with additional funding from the United States and Japan, and distributed with logistical support from Australia, national security adviser Jake Sullivan said Friday.

The announcement marked a significant step, showing that the Quad can “go from consultation and coordination to active cooperation in ways we can see,” said Tanvi Madan, director of the India Project at the Brookings Institution. It’s a “proof of concept.”

The vaccine commitment is “intended to show this coalition can provide important public goods to Southeast Asia, which should enhance their political influence in the region,” Lalwani said. China is now providing free vaccinations in the region.

The Quad concept dates to 2004, when the four countries came together for disaster relief efforts among their navies following the 2004 Indian Ocean earthquake and tsunami.

Officials from the countries met for the first time in 2007, setting the stage for future cooperation. But the initiative quickly broke down after leadership changes, including a new Australian prime minister who was distinctly cool to the idea, and the electoral loss of Japanese prime minister Shinzo Abe, a vocal proponent of the Quad.

The four countries are all democracies and maritime powers that have declared their common interests in a “free and open Indo-Pacific,” a term referring to the region encompassing the Indian and Pacific Oceans.

All four nations have seen their relations with China deteriorate — in some cases dramatically — in recent years. That, in turn, has provided fresh impetus.

“If China wasn’t challenging the rules-based order in the region, I’m not sure the Quad would exist, at least not in this form or with this urgency,” Madan said.

China has made clear its dislike for the idea of a new grouping, and views the Quad meetings as an attempt to encircle it. In 2018, China’s foreign minister, Wang Yi, said that talk of the Quad and an “Indo-Pacific” region might grab headlines but would dissipate “like sea foam.” Last year, Wang said the group was part of an effort to create “an Asian NATO” that would destabilize regional security.

The Quad is far from being an Asian NATO and still faces skepticism about its ultimate utility. In particular, some experts question whether the four countries can maintain a united front even as each pursues its own agenda with China.

Friday’s summit marks the start of a process.

“They’ve done the theater part of it, they need to fill it with substance,” said Shivshankar Menon, India’s former national security adviser.

The core issue uniting the group, he said, is maritime security in the Indian and Pacific oceans. That agenda includes joint naval exercises, disaster relief, anti-piracy efforts and environmental initiatives. On Friday, the leaders did not directly discuss threats from China’s maritime movements.

India’s stance will be the key determinant of the future of the Quad. While Japan and Australia are full-fledged allies of the United States, India is not. Instead, India has attempted to maintain a degree of strategic independence even as it has deepened its cooperation with the United States in recent years.

Over the past year, however, India’s relationship with China took a drastic turn for the worse. In June, the two countries engaged in their deadliest violence in decades when soldiers clashed at their shared, unofficial border. Twenty Indian soldiers and four Chinese troops were killed.

Both countries rushed tens of thousands of troops to the frontier in the mountainous region of Ladakh, producing a dangerous faceoff that continues, although a partial disengagement has occurred in certain areas.

Vijay Gokhale, who recently retired as India’s foreign secretary and previously served as ambassador in Beijing, wrote this week that the clash marked “an inflection point in the seventy-year relationship between Asia’s largest modern states.”

“Even the most dovish official or analyst in India has to now at least recognize that there’s something to the China threat and that it has to be taken seriously,” said Grossman, of Rand. “I think they’ve come a long way . . . and now, I think they’re just as strong a link as the other three.”

At Friday’s meeting, Indian Prime Minister Narendra Modi expressed his commitment to the partnership, calling the Quad “a force for global good.”

“Today’s summit meeting shows that Quad had come of age,” he said. “It will now remain an important pillar of stability in the region.”

Slater reported from New Delhi.