Throughout the era of Western imperialism in Asia, Siam remained the only nation in the region to avoid being colonized by foreign powers, although it was often forced to cede both territory and trade concessions in unequal treaties. The Siamese system of government was centralized and transformed into a modern unitary absolute monarchy in the reign of Chulalongkorn. In World War I, Siam sided with the allies, a political decision to amend the unequal treaties. Following a bloodless revolution in 1932, it became a constitutional monarchy and changed its official name to Thailand, which was an ally of Japan in World War II. In the late 1950s, a military coup under Field Marshal Sarit Thanarat revived the monarchy's historically influential role in politics. Thailand became a major ally of the United States, and played an anti-communist role in the region as a member of the failed SEATO, but since 1975, had sought to improve relations with Communist China and Thailand's neighbors. Apart from a brief period of parliamentary democracy in the mid-1970s, Thailand has periodically alternated between democracy and military rule. Since the 2000s, it has been caught in a series of bitter political conflict between supporters and opponents of Thaksin Shinawatra, which culminated in two coups, most recently in 2014 and the establishment of its current and 20th constitution and faces the ongoing pro-democracy protests.