This article originally appeared in War on the Rocks as part of a series examining maritime geography and strategic challenges in specific bodies of water across the world.

One Sea, Two Seas, Far Seas, Near Seas? For all the attention they receive as contested Indo-Pacific maritime regions, the strategic differences between East and South China Seas do not always get their due. Each of these bodies of water contains land features claimed by the People’s Republic of China and at least one ally or partner of the United States. To Beijing, the East and South China Seas are all part of its “near seas,” and China continues to take steps to assert control over this space as one unified maritime periphery — which we refer to colloquially as China’s “One Sea.” The disputed land features in these seas are small — islands, reefs, and rocks — but the economic, maritime, and security stakes associated with them are large. Countries around the East and South China Seas, however, are not taking China’s actions passively. In their own unique ways that reject the notion of a single “One China Sea,” these countries are adapting and exploring new methods to assert their own maritime rights.

Map of East China Sea and South China Sea

For those who view this region from afar, understanding the differences between the East and South China Seas is an important first step toward addressing the challenges posed by Beijing. Disputes in the East China Sea are primarily bilateral. Japan has expressly denied that China has any legitimate claims to the Senkaku Islands. In the South China Sea, disputes are inherently multilateral because of the large number of claimants and role of the Association of Southeast Asian Nations. It is also important to appreciate the rapidly evolving responses from nations contesting China’s claims, each of which employs unique approaches. In the Philippines, President Ferdinand Marcos Jr. has noted the need for a “paradigm shift” in terms of diplomatic approaches to the disputes — this stark rhetoric contributes to increased tension between Manila and Beijing, with the most recent incidents occurring in March. Vietnam has continued land reclamation activities, but also signed agreements to increase cooperation with the Philippines. Malaysia states that its “position on the South China Sea is consistent and remains unchanged” while quietly resolving some issues with neighbors such as Brunei. In the Taiwan Strait, which sits between the East and South China Seas, tensions between China and Taiwan continue to concern neighbors that could be drawn into a potential conflict. In the long term, understanding each country’s approach will be necessary for fully resolving the disputes. In the near term, U.S. policymakers will need to continue to tailor their approach in a way that acknowledges these differences while recognizing that the United States is not a claimant state.

With all this in mind, we argue that U.S. policymakers should maintain realistic expectations for dispute resolution, while also pushing for the (long overdue) Senate ratification of the U.N. Convention on the Law of Sea. The United States should continue to enable partners to ensure that all nations have access to the East and South China Seas.

East and South China Seas: Parallels

Clear similarities exist between the East and South China Seas. First, the two bodies of water have comparable geographies, and each play a key role in maritime shipping. Both are bound in one direction by mainland China and in the other by the first island chain, a series of archipelagoes extending from Russia’s Kamchatka Peninsula in the northeast down through Japan and Taiwan to the Malay Peninsula in the southwest.

Second, the East and South China Seas are rich in biological and energy resources. Both contain valuable fishing grounds that support the economic growth and food security of East and Southeast Asian countries. According to one estimate, the value of these fisheries is over $7 billion in the East China Sea and more than $15 billion in the South China Sea. In terms of oil and gas resources, the U.S. Energy Information Administration estimates that the hydrocarbon reserves in the East China Sea comprise at least 200 million barrels of oil and up to 2 trillion cubic feet of natural gas. In the South China Sea, the estimate is considerably higher: 11 billion barrels of oil and 190 trillion cubic feet of natural gas. Yet, due to increasing exploitation of their rich resources, the two seas face significant environmental concerns, facing challenges from pollution, natural habitat destruction, and severe depletion of fish stocks. In the South China Sea, coral reef cover is declining at a rate of 16 percent per decade.

Timeline of South China Sea and East China Sea
PRC Law on the Territorial Sea and Contiguous Zone
PRC ratifies UNCLOS
PRC Law on the Exclusive Economic Zone
China-ASEAN first agree to Declaration of Conduct
18th Party Congress Report declares China's objective to be a "maritime power"
Beijing condemns Tokyo's nationalization of Senkaku Islands
PRC declares Air Defense Identification Zone (ADIZ) in East China Sea
PRC begins large-scale reclamation activities in South China Sea
China-Vietnam oil rig crisis near Paracel Islands
PRC Defense White Paper specifies Strategic requirements of "near sea defense, far sea protection"
Beijing rejects international tribunal's ruling that PRC's South China Sea claims are invalid
China Coast Guard Law goes into effect authorizing lethal force against forign ships operating in PRC waters
China and Japan inaugurate defense hotline to prevent maritime and aerial clashes

Third, the two seas have seen increasing militarization, as countries competing for resources have more assertively enforced their maritime claims. In the South China Sea, this has included nations reclaiming land, constructing artificial islands, building military outposts on land features, conducting intelligence gathering and sovereignty patrols, and engaging in occasional altercations such as the 2014 China-Vietnam oil rig crisis. Although the East China Sea has not seen disputants build military infrastructure on contested land features, waters around the Senkaku Islands (which China calls the Diaoyu Islands) are increasingly the site of patrols by military and paramilitary forces. As tensions continue to simmer over Taiwan — which Beijing views as an inherent part of China — the waters in and around the Taiwan Strait have become stages for frequent presence and deterrence operations with escalatory potential.

Read more at War on the Rocks.

April Herlevi is a senior research scientist with CNA's China Studies Program and a non-resident fellow at the National Bureau of Asian Research.

Brian Waidelich is a research scientist with CNA's Indo-Pacific Security Affairs Program and president of the Yokosuka Council on Asia-Pacific Studies. He is currently deployed to Strike Group Five in Yokosuka, Japan, as part of the CNA Field Program.