The Philippines used to be just one of six governments competing for claims to the South China Sea, a tropical ocean that’s hot because of its resources. That country lags its rivals, especially China, in military might and scope of claim to the ocean that covers 3.5 million square kilometers. It’s not the most aggressive driller for whatever oil and natural gas lurk under the ocean floor, nor is it the major marine shipper. But in 2014 President Benigno Aquino’s government, bolstered by a strong legal claim to eastern parts of the sea and anger over China’s combative presence, asked the United Nations to arbitrate the sovereignty dispute. A U.N. panel agreed in October to do that. The outcome tipped to favor Manila will affect how claimants treat one another for years to come even if they don’t recognize the arbitration process.

Here’s how Manila’s U.N. gambit will change the whole maritime dispute.

In this photo released by the Taiwan Presidential Office, Taiwan’s President Ma Ying-jeou, second from right, arrives on his visit to Taiping Island, also known as Itu Aba, in the Spratly archipelago, south of Taiwan, Thursday, Jan. 28, 2016. (Taiwan’s Presidential Office via AP)

A simple reason first: The other claimants are listening to the Philippines. China, for example, after trying to ignore the U.N. request for arbitration in 2014, fought back in December with a position paper explaining its objections. China believes the U.N. panel isn’t entitled to hear the issue. In another example of attention to the Philippines, Taiwan President Ma Ying-jeou visited his government’s biggest holding in the ocean for his first time last month to remind the U.N. tribunal that the islet he stood on was a self-sustaining piece of land, not a rock or reef. If the U.N. tribunal rules it a reef, Taiwan could lose grounds for declaring an exclusive economic zone in the fishing-rich waters offshore. Taiwan is not a U.N. member but says it follows international law. On the day of Ma’s visit, the Philippine foreign affairs department asked all claimants to “refrain from actions that can increase tension in the South China Sea.”

Now a deeper reason why the Philippines will reshape the maritime dispute — which is Asia’s stickiest with occasional violent clashes since the 1970s: China will re-calibrate. The U.N. arbitration panel in Europe is tipped to favor the Philippines in calling the “nine-dash line” inconsistent with international conventions on maritime rights. China and Taiwan use that line to claim the ocean from their coasts south to Borneo. They cite Han Dynasty maps from more than 2,000 years ago in forming the line. China says it won’t recognize the U.N. body’s decision. But it actually will, or risk being seen increasingly as a bully in Asia. It might start negotiating one-on-one with the Philippines and others, such as ever-angry claimant Vietnam, to shore up a reputation soiled by the landfill expansion of numerous disputed reefs. If China doesn’t attempt amends, Vietnam and the Philippines will ally ever closer to Japan and the United States, threatening China’s maritime claims as well as its big-guy status in Asia. U.S. officials want access to the sea so they can contain China’s rise and protect marine shipping lanes good for American companies. “There is already considerable discussion about how China’s actions are challenging its claim as benevolent neighbor to Southeast Asia,” says Carl Baker, director of programs with the think tank Pacific Forum Center for Strategic and International Studies.

Another long-term reason for how the Philippine legal action will change things: Support from the U.N. tribunal will empower governments with less aggressive maritime claims to work together and press China harder to sign agreements. Malaysia and Brunei also call parts of the South China Sea their own but seldom speak out. The Southeast Asian players feel frustrated that China won’t agree to strengthen or replace a 14-year-old code of conduct. A new code would be aimed at preventing clashes in an ocean that’s crawling with fishing boats, coast guard vessels and oil rigs. China uses its global clout to stop Taiwan from pursuing regional diplomacy, as well. A favorable U.N. arbitration outcome would strengthen the Philippine “negotiating posture,” says Ramon Casiple, executive director of Philippine advocacy group Institute for Political and Electoral Reform. Manila, he says, will “aggressively pursue a unified ASEAN (pan-Southeast Asia) China policy, particularly on the maritime claims in the South China Sea.”