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Bangkok's economy gradually expanded through busy 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.
By then, many public and social issues had emerged, among them the strain on infrastructure reflected in the city's notorious traffic jams.
Five rapid transit lines are now in operation, with more systems under construction or planned by the national government and the Bangkok Metropolitan Administration.
Because of its strategic location near the mouth of the river, the town gradually increased in importance.
Disproportionate urban development led to increasing income inequalities and unprecedented migration from rural areas into Bangkok; its population surged from 1.8 million to 3 million in the 1960s.
Following the United States' withdrawal from Vietnam in 1973, Japanese businesses took over as leaders in investment, and the expansion of export-oriented manufacturing led to growth of the financial market in Bangkok.
It was subject to Japanese occupation and Allied bombing during World War II, but rapidly grew in the post-war period as a result of United States developmental aid and government-sponsored investment.