The South China Sea territorial disputes between China and its neighbours can be partly traced to an internal map published by the Republic of China government in 1947 that included an “eleven-dash line” enclosing much of the waters.

China did not explain the significance of the line at the time. It was adopted by the People’s Republic of China government after the Communists came to power two years later. Then, in 1953, China unveiled a new map with a “nine-dash line” that covered a slightly smaller area of the South China Sea, losing two dashes that ran through the Gulf of Tonkin between China and Vietnam.

For a while, the line was largely ignored and the situation in the South China Sea was relatively calm. But everything changed when the UN released a study in 1968 that suggested there were significant hydrocarbon resources in the waters.

That triggered renewed interest in maritime territorial issues. Over the following decades, Vietnam, the Philippines, Malaysia, Taiwan and China all made various moves to occupy or claim islands and features in the South China Sea.

The line remained an irritant during this period. But it really emerged as a major point of contention in 2009 when China included it with a submission to the UN, essentially presenting it formally to the world for the first time. In 2012, China then angered its neighbours by printing the line on maps in its citizens passports.

The US remained silent on the “nine-dash line” until February 2014 when Daniel Russel, a top state department official, said China should clarify its meaning.

Kurt Campbell, the former Obama administration top diplomat for east Asia, says the US is now taking a tougher stance because of China’s actions. He says the US previously played a less visible role because the Association of Southeast Asian Nations argued that US intervention would complicate negotiations with China.

“Asean has reached a place where they have become somewhat frustrated by the lack of progress,” says Mr Campbell.

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