After the Second World War, the USA became a new foreign patron, more intrusive than anything Siam had experienced in the colonial era. While Britain had focused on its colonies and never taken more than peripheral interest in Siam, the USA seized on Thailand as an ally and base for opposing the spread of communism in Asia. To build Thailand's capability for this role, the USA helped to revive and strengthen the military rule, which had faltered at the close of the Second World War. To consolidate Thailand's membership of the ‘free world’ camp in the Cold War, the USA promoted ‘development’, meaning primarily economic growth through private capitalism. To achieve ‘national security’, US funding helped to push the mechanisms of the nation-state more deeply into society than before.

Under this regime, a new elite emerged consisting of ruling generals, senior bureaucrats, and the heads of new business conglomerates. Strengthened by the ideology of development and unconstrained by democracy, business was able to exploit both people and natural resources on a new scale. The countryside was transformed again, by driving the agrarian frontier through the upland forests, and subjecting the smallholder decisively to the market. Against this backdrop, the old Thai social order faded into history.