The semi-presidential system includes a bicameral legislature consisting of a 100-member Senate and a 342-member National Assembly. The President is the Head of State and the Commander in Chief of the Armed Forces and is elected by an electoral college. The prime minister is usually the leader of the largest party in the National Assembly. Each province has a similar system of government with a directly elected Provincial Assembly in which the leader of the largest party or alliance becomes Chief Minister. Provincial Governors are appointed by the President. The Pakistani military has played an influential role in mainstream politics throughout Pakistan's history, with military presidents ruling from 1958–71, 1977–88 and from 1999 onwards. The leftist PPP, led by Zulfikar Ali Bhutto, emerged as a major political player during the 1970s. Under the military rule of Muhammad Zia-ul-Haq, Pakistan began a marked shift from the British-era secular politics and policies, to the adoption of Shariat and other laws based on Islam. During the 1980s, the anti-feudal, pro-Muhajir Muttahida Qaumi Movement (MQM) was started by unorthodox and educated urban dwellers of Sindh and particularly Karachi. The 1990s were characterized by coalition politics dominated by the PPP and a rejuvenated Muslim League.
In the October 2002 general elections, the Pakistan Muslim League (Q) (PML-Q) won a plurality of National Assembly seats with the second-largest group being the Pakistan Peoples Party Parliamentarians (PPPP), a sub-party of the PPP. Zafarullah Khan Jamali of PML-Q emerged as Prime Minister but resigned on 26 June 2004 and was replaced by PML-Q leader Chaudhry Shujaat Hussain as interim Prime Minister. On 28 August 2004 the National Assembly voted 191 to 151 to elect the Finance Minister and former Citibank Vice President Shaukat Aziz as Prime Minister. Muttahida Majlis-e-Amal, a coalition of Islamic religious parties, won elections in North-West Frontier Province, and increased their representation in the National Assembly.