You need to adjust your timescales. "Settled for hundreds of years"? No. Settled for tens of thousands of years. In many places the shoreline moved three feet per year, when water was rising fastest; the beach one played at as a child was wholly gone by adulthood. The grandparents' ancestral shoreside village was underwater.
People could not just move inland; other people already lived there. Australians still keep careful oral records of negotiated resolutions of conflicts over living space when Sahel, between Australia and New Guinea, was inundated.
Between where Indonesian islands are now, and for hundreds of miles off the coast of Viet Nam all the way to Korea, were millions of square miles of prime habitat ("Sundaland"), also for tens of thousands of years. Every tribe there had to find somewhere else to live.
People could not just move inland; other people already lived there. Australians still keep careful oral records of negotiated resolutions of conflicts over living space when Sahel, between Australia and New Guinea, was inundated.
Between where Indonesian islands are now, and for hundreds of miles off the coast of Viet Nam all the way to Korea, were millions of square miles of prime habitat ("Sundaland"), also for tens of thousands of years. Every tribe there had to find somewhere else to live.