Malaysia has rejected the latest edition of the ‘standard map of China’ that lays claim to almost the entire South China Sea, including areas lying off the coast of Malaysian Borneo.
Tensions have been rising in the strategically important waters as China has become increasingly assertive in its claim despite a 2016 international court ruling that its so-called ‘nine-dash line’ was without merit and superseded by the 1982 United Nations Convention on the Law of the Sea (UNCLOS).
In recent years, it has built military outposts on rocky outcrops and deployed its coast guard and maritime militia, which has sometimes led to confrontations with other claimants, including Malaysia and the Philippines. Vietnam, Brunei and Taiwan also have claims to the sea.
China did make some change by broadening its territorial claims (both in India and South China Sea) with the release of a new map.
With the nine-dash line, you asked a great (and extremely contested) question. The short answer is that China isn’t the only country with historical evidence to support its claim to the area. Both Vietnam and the Philippines, for example, can also make a case.
In fact, I would point you to Philippines v. China. In this case, on 12 July 2016, an arbitral tribunal constituted under the United Nations Convention on the Law of the Sea (UNCLOS), of which China is a member, concluded that: “… while it would not “rule on any question of sovereignty … and would not delimit any maritime boundary”, China’s historic rights claims over maritime areas (as opposed to land masses and territorial waters) within the “nine-dash line” have no lawful effect unless entitled to under UNCLOS.” (https://en.wikipedia.org/wiki/Philippines_v._China).
I’m not a lawyer nor geopolitical analyst but I recall that regardless of the actual merits of the claim, China or any country must insist on disputing territorial ownership, so as not to tacitly concede that it does not belong to them. The actual resolution of the dispute might not be as relevant as the mere presence of a dispute itself. Not sure if this is still the right take, happy to be corrected by someone more knowledgeable.