Bangladesh inherited the provincial government under which first the Dominion, then Republic, of Pakistan was governed, a parliamentary system based on the Westminster model with a unicameral legislature. Following this model, the constitution of December 1972 established a unitary, democratic republic, with an indirectly elected president as nominal head of state and a prime minister as head of government and chief executive. The prime minister and his government are responsible to a unicameral legislature—the National Assembly—elected no less frequently than every five years and composed of 300 members. (A constitutional amendment reserving 30 additional parliamentary seats for indirect election of women expired in May 2001.) The constitution incorporated four basic principles of state policy: nationalism, secularism, socialism, and democracy. With considerable controversy, because of its impact on the nearly 17% of the population which is non-Muslim, Islam replaced secularism as a state principle by constitutional amendment in 1977.
The constitution was amended in 1975, at the initiative of Prime Minister Mujibur Rahman, to abrogate most guarantees of civil liberties, to establish a one-party polity, and to make the presidency, rather than the prime ministership, the chief executive of the government. Mujib's assassination later that year, and the countercoup that occurred three months later resulted in a four-year year suspension of the constitution by Bangladesh's martial law ruler, Gen. Zia-ur Rahman.
Rahman himself was assassinated in 1981, and in the turmoil that ensued, General H. M. Ershad seized power. Ershad declared himself president in 1982, and held office until 1990, when increasing antigovernment protests and violence resulted in his resignation. He was later jailed on corruption charges. The interim government then conducted what most observers regard as the most free and fair elections ever held in Bangladesh, in 1991.
Among her first acts as prime minister (the first woman to hold that position in Bangladesh), Begum Khaleda Zia-ur Rahman, widow of General Rahman and the head of his Bangladesh Nationalist Party, reversed from her former position in favor of retaining a strong presidential system to restore the parliamentary system of 1972 and to return to the prime ministership the powers removed by Mujib in 1975. She led the campaign with strong Awami League support, which resulted in overwhelming parliamentary approval of a constitutional amendment. Kahleda Zia was forced to step down in March 1996, after two years of political turmoil following an opposition boycott of Parliament and elections. The opposition AL, which claimed the BNP had rigged two elections, was swept into power in the internationally monitored elections of June 1996. Sheikh Hasina Wajed then formed a coalition majority in Parliament with the Jatiya Party. By September 1996, with several victories in by-elections, the Awami League controlled an absolute majority of seats in Parliament. The government was thus unaffected by the Jatiya Party's withdrawal from the coalition in March 1997.
Parliamentary elections held 1 October 2001 resulted in a return of Hasina's bitter enemy Kahleda Zia to power. The BNP took 201 seats, the AL held 62, Jamaat-e-Islami held 18, and the Ershad faction of the Jatiya Party took 14 seats. The majority BNP government aligned with three of the smaller parties, Jamaat-e-Islami, Islami Oikya Jote, and the Naziur faction of the Jatiya Party. Elections are next to be held before October 2006. The Jamaat-e-Islami party is sympathetic to Osama bin Laden, a position that was controversial, especially after the 11 September 2001 terrorist attacks on the United States attributed to him. Zia attempted to quell domestic and international unease resulting from this position, asserting that Bangladesh would not become a fundamentalist Islamic state. However, her three coalition partners advocate replacing Bangladesh's secular laws with Islamic law, or Shari'ah .