Answer
Plaek Phibunsongkhram was Pridi Banomyong's long-time rival. Pridi was a democrat who believed in liberal democracy and constitutional monarchy, while Phibun was a nationalist who believed in authoritarianism and military rule. The two men were constantly at odds with each other, and their rivalry was one of the major factors that led to the political instability that plagued Thailand in the 1930s and 1940s.