The new official border was called the Radcliffe Line, created in 1947 by a British barrister, Sir Cyril Radcliffe. The two parts of Pakistan were separated by over 2000 kilometers of Indian landmass, and cultural and linguistic differences. By 1971, this political situation had become untenable, and East Pakistan cleaved off to become the sovereign nation of Bangladesh.
The 1947 partition was based on religion – India was to be a Hindu majority nation, and Pakistan was to be a Muslim majority nation. While East and West Pakistan were both Muslim majority, West Pakistan was dominated by Urdu speaking people and East Pakistan was dominated by Bengali speaking people. Additionally, there were political and economic factors that created an unbridgeable rift between East and West Pakistan, leading East Pakistan to declare its independence from West Pakistan.