This chapter examines the impact of US-Sino relations on regional maritime security within the context of recent developments in the South China Sea. President Aquino's decision to sign an administrative order on 5 September 2012 to rename part of the South China Sea as the Western Sea of the Republic of the Philippines as well as the order to publish a new map to include Kalayaan and the Scarborough Shoal as part of the Western Sea. Events in Africa and Latin America, where China has established a very strong economic presence in the last decade or so, have also shaped US-Sino relations. US-Sino competition has caused temperatures to rise in the South China Sea. The Nation of Thailand warns in a recent editorial that: If the current tension continues in South China Sea, especially between the Philippines and China, it could lead to an all-out war. This is not an alarmists warning but a real concern.