The subsequent Ren’ai Shoal Incident and Drilling Platform 981 Standoff further aggravated the situation. As its landing craft aground at Ren'ai Shoal was disintegrating, the Philippines kept looking for opportunities to start construction projects to get the shoal under its control. China has kept a watchful eye on the activities. In March 2014, China discovered that some Philippine warships were transporting supplies to Ren'ai Shoal and immediately intercepted them, which lead to a standoff between both sides. The Philippines incited a storm of media coverage of the incident, trying to elicit global attention and the US’s intervention.

In May 2014, a drilling operation by the HYSY 981 rig was completed inside the contiguous zone of China's Xisha Islands. The drilling was performed 17 nautical miles from the south of Zhongjian Island (Triton Island) from May 2 to August 15, during which it was harassed by hundreds of vessels sent by the Vietnamese government, resulting in intensified situation with multiple chases and even collisions between the China Coast Guard flotilla and the Vietnamese law enforcement vessels.

In 2013, in view of the changing situation in the South China Sea, and to meet the civil and defense needs on the islands and to defend its sovereignty, China launched reclamation projects on its controlled Nansha islands. As all of these islands are far away from the international navigation routes, there was no question of these projects having any impact on the freedom of navigation. But the US and the Philippines kept accusing China and hyping the issue. In response to the concerns, China's Foreign Ministry spokesperson Hua Chunying made a detailed explanation at a press conference held on April 9, 2015: The Chinese government has been carrying out maintenance and construction work on some of the garrisoned Nansha islands and reefs with the main purposes of optimizing their functions, improving the living and working conditions of personnel stationed there, better safeguarding territorial sovereignty and maritime rights and interests, as well as better performing China's international responsibility and obligation in maritime search and rescue, disaster prevention and mitigation, marine science and research, meteorological observation, environmental protection, navigation safety, fishery production service and other areas. The relevant construction, which is well within China's sovereign responsibility. It does not impact or target any country. [xv] It is recently reported that a series of projects are underway to construct facilities that can provide public service, like lighthouses, automatic weather stations, marine observation centers and marine research institutes. Five lighthouses for navigation safety have been built, and four of them have been put into use.

China’s actions have not been fully understood by its neighbors who expressed concerns. The US also stepped up its intervention, buzzing over China’s island reclamation projects using rhetoric like “reaching too far and too fast” and “islands militarization” to pile pressure on China, and even sending ships to sail near the Nansha and Xisha Islands. All these were perceived in China as serious security challenges.

From the perspective of many Chinese people, the US is the invisible hand behind the rising tension in the South China Sea. First, the US is increasingly targeting at China as it steps up its Asia-Pacific rebalance strategy. In 2013, the US announced to reinforce its military presence in the Asia-Pacific region by deploying 60% of its fleet and 60% of its overseas air force to the region by 2020. [xvi]Also, the US military has purported to be threatened by “China’s anti-access and area denial efforts”, and actively promoted some operational concepts like Air-Sea Battle, with China as a main target. These moves have undoubtedly further complicated and intensified the situation in the South China Sea and in the Asia-Pacific region as a whole. Many Chinese scholars start to suspect that the US may be creating illusionary threats and crises in the region which can turn into a self-fulfilling prophesy.

Since 2014, the US has made clearer responses to China in the South China Sea, in postures of direct intervention in the disputes and often in favor of other claimants, especially its own allies.

On February 5, 2014, US Assistant Secretary of State for East Asian and Pacific Affairs Daniel Russel said at a congressional hearing that China was “lack of clarity with regard to its South China Sea claims has created uncertainty, insecurity and instability in the region.”[xvii] He also urged China to clarify its nine-dash line claim. This was the first explicit and official comment made by the US to challenge China on the South China Sea issue. And obviously the US was well aware that, as the Nansha Islands dispute was still unsettled, any attempt to clarify the dash line or maritime claims would only lead to an escalation of tensions. In the same month, US Chief of Naval Operations (CNO), Admiral Jonathan Greenert announced US's support for the Philippines in the event of a China-Philippines conflict. [xviii] This is the toughest stance expressed by the US in the China-Philippine dispute. At the Post Ministerial Conference of the ASEAN Foreign Ministers' Meeting in Naypyidaw in August 2014, US Secretary of State John Kerry directly called for a moratorium on land reclamation, building on disputed islands, and actions that might further escalate disputes.

The US started to opt for a cost-imposing strategy against China, meaning to make it more costly for China to take any actions in the South China Sea by resorting to political, diplomatic, public opinion and military means, so as to force China to pull back without inciting arms confrontation.[xix] In 2015, the US released three strategic security documents, titled Forward, Engaged and Ready: A Cooperative Strategy for 21st Century Seapower, National Security Strategy, National Military Strategy and Asia-Pacific Maritime Security Strategy, respectively, all of which talked about the South China Sea issue at fairly great length, and asserted that the US would make China pay the price.

From the Chinese perspective, as well as undermining the US credibility as a potential mediator, the US's dramatically altered policy on the South China Sea has heightened China's fears that its interests would be further undermined, thus inspiring its determination and measures to defend them.

Echoing its policy readjustments, the US has accelerated provocative and coercive actions that are clearly targeted at China. For example, the US’s surveillance at the Nansha Islands and its surrounding waters have intensified. The number of sorties flown by the US planes to conduct close-in reconnaissance at the South China Sea Islands has increased from about 260 in 2009 to over 1,200 in 2014. [xx] Also, as a way to flex its muscle and assert freedom of navigation, the US keeps sending ships to sail within 12 nautical miles of the Nansha Islands or even the non-disputed Xisha Islands. On October 27, 2015, the USS Lassen navigated within 12 nautical miles of Zhubi Reef (Subi Reef). On January 30, 2016, the USS Curtis Wilbur trespassed China’s territorial waters near Zhongjian Island. Quite different from its usual practice, the US media began to buzz over these events. US Pacific Command commander Harry Harris even openly declared to take more sophisticated and wide-ranging activities in the future, and send warships to the South China Sea about twice a quarter. [xxi]

Other deterrent actions taken by the US include the followings: In July 2015, the new commander of the US Pacific Fleet Admiral Scott Swift joined the surveillance mission on board the ASW P-8A Poseidon to conduct close-in reconnaissance at the South China Sea; on November 5, US Secretary of Defense Ashton Carter cruised on the USS Roosevelt, and when he began to deliver a speech on board, the carrier was churning through the disputed waters about 150-200 nautical miles south of the Nansha Islands and about 70 nautical miles north of Malaysia; on November 8 and 9, two US B-52 strategic bombers flew near the Chinese islands under construction; and during his visit to the Philippines on April 15, 2016, Carter landed aboard the aircraft carrier USS John C. Stennis and joined a patrol in the South China Sea. US warships and planes also frequently conducted “innocent passage” through China’s territorial waters and airspace.

The US has also sought to strengthen its alliance system and forces network surrounding the South China Sea. Since the implementation of the Asia-Pacific rebalance strategy, the US has been stepping up deployment of forces around the South China Sea rim, including the Australian port of Darwin, the Changi Naval Base in Singapore, the Philippines and Malaysia. The US is also enhancing cooperation with Malaysia, Indonesia and Vietnam to conduct intelligence gathering and enhance maritime domain awareness capabilities in the region, and expanding military support to some claimants in the dispute like the Philippines and Vietnam, to help improve their reconnaissance, patrol control and anti-access capacity. In March 2016, the US and the Philippines announced at their sixth annual Bilateral Security Dialogue that the US forces were allowed to use five Philippine military bases. In April 2016, the US and the Philippines conducted again the Shoulder-to-Shoulder exercises in the South China Sea, with more targeted items like retaking over islands, oil rig defense, etc., obviously aiming at disputes in the South China Sea.