Bangkok's economy gradually expanded through international trade, first with China, then with Western merchants returning in the early-to-mid 19th century. As the capital, Bangkok was the centre of Siam's modernization as it faced pressure from Western powers in the late-19th century. The reigns of Kings Mongkut (Rama IV,  1851–68) and Chulalongkorn (Rama V,  1868–1910) saw the introduction of the steam engine, printing press, rail transport and utilities infrastructure in the city, as well as formal education and healthcare. Bangkok became the centre stage for power struggles between the military and political elite as the country abolished absolute monarchy in 1932.