Pakistan's political experience is essentially related to the struggle of Indian Muslims to regain the power they lost to British colonisation. Pakistan is a democratic parliamentary federal republic, with Islam as the state religion. The first constitution was adopted in 1956 but suspended by Ayub Khan in 1958, who replaced it with the second constitution in 1962. A complete and comprehensive constitution was adopted in 1973, it was suspended by Zia-ul-Haq in 1977 but reinstated in 1985. This constitution is the country's most important document, laying the foundations of the current government. The Pakistani military establishment has played an influential role in mainstream politics throughout Pakistan's political history. The periods 1958–1971, 1977–1988, and 1999–2008 saw military coups that resulted in the imposition of martial law and military commanders who governed as de facto presidents. Today Pakistan has a multi-party parliamentary system with clear division of powers and checks and balances among the branches of government. The first successful democratic transition occurred in May 2013. Politics in Pakistan is centred on, and dominated by, a homegrown social philosophy comprising a blend of ideas from socialism, conservatism, and the third way. As of the general elections held in 2013, the three main political parties in the country are: the centre-right conservative Pakistan Muslim League-N; the centre-left socialist PPP; and the centrist and third-way Pakistan Movement for Justice (PTI).