With the Partition of Bengal (as part of the wider Partition of India) in 1947, Dhaka became the capital of East Bengal (1947–1955) and East Pakistan (1955–1971). It hosted the largest legislature in Pakistan, as East Bengalis comprised the majority of the new state's population. Dhaka's urban population increased dramatically because of Muslim migration from across Bengal and other parts of the subcontinent. Dhaka began to see rapid urban expansion from the 1950s. The East Pakistan Stock Exchange Association was formed on 28 April 1954 and later became the Dhaka Stock Exchange. Orient Airways, founded by the East Pakistani industrialist Mirza Ahmad Ispahani, began the first commercial flight between Dhaka and Karachi on 6 June 1954. The airline later evolved into Pakistan International Airlines. The Dhaka Improvement Trust was established in 1956 to coordinate the city's development. The first master plan for the city was drawn up in 1959. Several countries opened consulates in Dhaka, including the United States, India, the United Kingdom, the Soviet Union and China. The Southeast Asia Treaty Organization established a research center (now called ICDDR,B) for combating disease in 1960.