Government is essentially an instrument for the delivery of public goods (including social order. What would motivate a subset of a territory under one government to desire self-government?
The motivation arises when there is a failure in the existing government, and a reasonable hope that self-government may improve matters. In the status quo, public goods may fail to be delivered. Common pool resources may be mismanaged from the parochial perspective; minerals, forests, fisheries, and the like may be mined out to benefit the larger territory with little benefit to the local economy. Third, the local populace may find themselves on the short end of coercive resource pooling - as in the taxation system (the story of the US of A), and other levies such as wartime draft. Such failures can be attributed to deliberate design to exact surplus, or to sheer neglect due to the demands of maintaining a government bureaucracy over a large territory.
National security (a public good provided by government) implies protection of the state not only from external threat, but also internal division. Sheer exertion of force is costly, hence other means of maintaining social order are desirable. The most ubiquitous of these is the cradle-to-grave socialization into the body politic. (Iniibig ko ang Pilipinas. Ito ang aking lupang sinilangan. Ito ang tahanan ng aking lahi....)
Was the independence of the Philippines from the United States beneficial to the country? (Incidentally what Filipinos celebrated today was Independence from Spain.) I think the issue is moot: the United States would have granted independence anyway, after doing a cost-benefit analysis. Maintaining control over the country (despite its known natural treasures) would have been a net drain of American resources, for dubious benefits (on their part). I doubt whether US administration would have been able to replicate the rapid improvement of living standards of the East Asian high performers, given American niggardliness at providing subsidies, welfare, and capital outlays for backward regions.
Filipino self-rule really had a better chance at poverty reduction. Unfortunately we have so far flubbed it by remaining stuck in a blame-mongering, backward-looking, insular mentality. There's a sort of historical inertia, where earlier realities are expected to prevail until Kingdom come. So if the colonial masters were oppressing us before, heck our backwardness now is because of continued dominance by the US-IMF-WB-WTO evil imperalist neocolonial structures.
Real independence starts with critical thinking.