Prior to 1947, Bangladesh was part of British India. In 1947, West Pakistan and East Bengal separated from India and jointly became the new country of Pakistan. East Bengal became East Pakistan in 1955. East Pakistan seceded from its union with West Pakistan on 16 December 1971, and was renamed the People's Republic of Bangladesh.
The country's legal system is based on English common law. The constitution of Bangladesh entered into force on 16 December 1972 and has been amended, most recently in 2004. The constitution is available at Bangladesh's government website at: <http://www.pmo.gov.bd/constitution/index.htm>, a pdf copy of which is attached.