The western wing eventually included thirteen princely states, one union of states, Gwadar enclave, Gilgit agency and parts of Kashmir: Simmering tensions between the eastern and western wings of Pakistan led to the One Unit policy announced by Prime Minister Muhammad Ali Bogra.

West Pakistan annexed the former Omani enclave of Gwadar (on the Balochistan coast) in 1958 as part of Kalat division.

In 1963 the Trans-Karakoram Tract was transferred by treaty from Gilgit Agency to China under the provision that the settlement was subject to the final solution of the Kashmir dispute.

Thus from 1955 to 1970, Pakistan comprised two provinces: The One Unit policy was regarded as a rational administrative reform to reduce expenditure and eliminate provincial prejudices.

However the military coup of 1958 signalled troubled times for the two-province system as the office of Chief Minister of West Pakistan was abolished by President Ayub Khan to be replaced by Governor's rule.

The Federally Administered Tribal Areas were formed from parts of the North West Frontier Province districts of Peshawar and Dera Ismail Khan in 1975.