In nearly ten years after the introduction of the DOC, China was the only keen abider of the document. It refrained from taking actions that might escalate the dispute in the South China Sea, and kept pushing for peace and cooperation and joint development in disputed areas. By contrast, Vietnam, Malaysia, the Philippines and some other ASEAN countries were half-hearted about the DOC. They kept on transforming and expanding occupied islands, reinforcing their administrative management of them, and accelerated the development of oil and gas in surrounding waters. They also made occasional arrests of Chinese fishermen working in these waters. One common efforts of these countries is to solidify their illegal occupation and extend the territorial dispute to the maritime sphere. What they were trying to do was more of denying the existence of the disputes than shelving them. This continuously enraged the Chinese public and media, eliciting sustained attention.
Vietnam was the most active violator of the DOC. For example, in April 2003, it held a commemoration to celebrate the 28th anniversary of the "Liberation of the Nansha Islands". In June, it signed a secret pact with Indonesia on the delimitation of continental shelf under the South China Sea. In April 2004, it organized the first commercial tour to the Nansha Islands. In early 2005, it published a revised map of Vietnam, which included China's Xisha and Nansha Islands into its Khanh Hoa Province. In early 2006, Vietnam and Malaysia set up a navy hot-line to coordinate resource development and settlement of their disputes about the Chinese islands. In April, it started another bidding round for oil blocks in surrounding waters, and announced cooperation with a third party on building natural gas transmission pipelines in the Nansha Islands. In May 2007, it conducted an extensive geological survey in surrounding waters using a charted foreign surveying ship; a month later, it held elections of "National Assembly representatives" on some of the occupied Nansha islands.
In April 2003, Malaysia sent four flotillas totaling 11 surveying vessels to the waters around Nantong Reef (Louisa Reef) to conduct prospecting operations; in May, it organized an international maritime challenge in waters around Danwan Reef and approved for the first time commercial tours to Yuya Shoal organized by travel agencies. In November 2004, it published stamps showing a Malaysian map with newly included Nansha islands. In August 2008, Malaysia's Defense Minister landed on Danwan Reef with some 80 journalists to declare "sovereignty".
In April 2003, the Philippines celebrated the 25th anniversary of the establishment of Kalayaan Municipality on Zhongye Island. In June 2006, it started to renovate and upgrade the air strip and other facilities on the island. In March 2008, it set up satellite communications facilities on some of the occupied islands and shoals.
But it must be admitted that despite a continuing tug-of-war in the South China Sea, the general situation was under control before 2009. Soon thereafter, things became more complicated, mostly due to an official deadline set by the UN Commission on the Limits of the Continental Shelf (CLCS), according to which relevant states should submit claims over a continental shelf extending the 200 nautical miles from its territorial sea by May 15, 2009. An even greater factor is the introduction of the American Asia-Pacific rebalancing strategy.
Shortly after taking office in January 2009, the Obama administration signaled that it would correct the Bush administration's misplaced foreign policy by shifting the US's strategic priority to the Asia-Pacific region, which obviously contributed to the confidence of the other claimants in the South China Sea to challenge China.
Between January and February 2009, the Philippines' House of Representatives and Senate adopted the Territorial Sea Baselines Bill, which claims China's Huangyan Island and some islands and reefs in the Nansha Islands as Philippine territory. On May 6, choosing to ignore the outstanding territorial and maritime delimitation disputes in these waters, Vietnam and Malaysia jointly submitted to the CLCS information on the outer limits of the continental shelf beyond 200 nautical miles in the South China Sea. On May 7, Vietnam separately submitted to the CLCS information on the outer limits of the continental shelf beyond 200 nautical miles, claiming sovereignty over China's Xisha and Nansha Islands. Under such circumstances, China had no choice but to submit to the CLCS the preliminary survey findings on the outer limits of its continental shelf beyond 200 nautical miles, in order to prevent further undermining of its own interests.
Meanwhile, US started to have frictions with China in the South China Sea. 2009 alone saw at least five confrontational incidents between US and Chinese ships, with the USNS Impeccable incident being the most conspicuous.