I'm glad that you bring this up. This dispute between Malaysia and the Philippines is real, and has been severely under-reported. While China is often hyped up as the threat to ASEAN. There are so many more disputes going on within ASEAN itself. This dispute over the Malaysian state of Sabah is one of them. There was one flashpoint: an area called Lahad Datu. Let's talk about Malaysia's history in this dispute.
The one thing I would disagree with you is that it is not the US that kept Malaysia from balkanizing, but actually the British. The British, along with some Commonwealth nations had extensive military presence in Malaysia during the Malayan Emergencies from 1948 - 1989 to fight the various communist insurgency. That kept Malaysia as a defacto client state of the British. Kinda like the French military presence in Mali. There were curfews, martial laws, propaganda, emergency laws, and powerful British influence in Malaysian politics. That, I believe is what truly kept Malaysia together throughout it's early years.
Except for Singapore, which was actually demographic engineering. The main purpose of which was to exile a large part of the Chinese population out of Malaysia, and make the Malay population at that time, the overall majority. The British were in Red Scare hysteria, so they distrusted the Chinese as communists. While the Malay elites are just racists. Both didn't want the Chinese vote their way into power. The British preferred to have the much more obedient Malays rule over the greater part of Malaysia. While the Malay elites want to become the ultimate rulers of Malaysia. The excess Chinese population were exiled onto an island called Singapore with nothing much, but swampland, old British bases, and a port. Then the rest is history.
Malaysia, just like India, was a nation that was put on the map by the British. Blessed by the British with a Westminster system, British education, and colonial-era infrastructure to inherit. That is how I understand the identity crisis of Indian chauvinists. There was never a unified 'Malaysia' prior to British colonial rule. West Malaysia was formed from a hodgepodge of Malay Sultanates, and land concessions to the British from Siam (known as Thailand today) and the Dutch (their colony of Malacca). East Malaysia on Borneo, was formed from land concessions from the Brunei Sultanate and Sulu Sultanate to the British. In addition to further British expansion into Borneo to claim more territories from petty kingdoms. It's actually more complicated than that, but I'll keep it simple and call all of the colonialists as the British.
So Malaysia's territorial claim on Sabah is a result of British colonialism. The Sulu Sultanate's claim on Sabah does predate the Malaysian claim. So their claim is stronger. But there is a problem: the Sulu Sultanate does not exist today. So how exactly did the Philippines inherited the territorial claims of the Sulu Sultanate? I am not familiar with Filipino history. So I have to ask this question to you,
@ansy1968.