Nine-dash line in the context of "Spratly Islands"

The first island chain is the first string of major Pacific archipelagos out from the East Asian continental mainland coast. It is principally composed of the Kuril Islands, the Japanese archipelago, the Ryukyu Islands, Taiwan (Formosa), the northern Philippines, and Borneo, hence extending all the way from the Kamchatka Peninsula in the northeast to the Malay Peninsula in the southwest. The first island chain forms one of three island chain doctrines within the island chain strategy in the U.S. foreign policy. It is considered a strategic military barrier to accessing the wider Pacific Ocean given the relative shallowness of waters to the west of the first island chain, which has important implications for submarine detection.

Much of the first island chain is roughly situated in waters claimed by the People's Republic of China (PRC). These include the South China Sea, within the disputed nine-dash line, as well as the East China Sea west of the Okinawa Trough.

Brunei, Indonesia, Malaysia, the Philippines, the People's Republic of China (PRC), Taiwan (Republic of China/ROC), and Vietnam have conflicting island and maritime claims in the South China Sea. The disputes involve the islands, reefs, banks, and other features of the region, including the Spratly Islands, Paracel Islands, Scarborough Shoal, and various boundaries in the Gulf of Tonkin. The waters near the Indonesian Natuna Islands, which some regard as geographically part of the South China Sea, are disputed as well.

An estimated US$3.36 trillion worth of global trade passes through the South China Sea annually, which accounts for a third of the global maritime trade. 80 percent of China's energy imports and 40 percent of China's total trade passes through the South China Sea. Claimant states are interested in retaining or acquiring the rights to fishing stocks, the exploration and potential exploitation of crude oil and natural gas in the seabed of various parts of the South China Sea, and the strategic control of important shipping lanes. Maritime security is also an issue, as the ongoing disputes present challenges for shipping.