Immigration, both from within and outside the country, is regarded as one of the main factors that has contributed to urbanisation in Pakistan. One analysis of the 1998 Pakistan Census highlighted the significance of the Partition of India in the 1940s in the context of understanding urban change in Pakistan. During the independence period, Muslim Muhajirs from India migrated in large numbers and shifted their domicile to Pakistan, especially to the port city of Karachi, which is today the largest metropolis in Pakistan.
Migration from other countries, mainly those in the neighbourhood, has further catalysed the process of urbanisation in Pakistani cities. Of particular interest is migration that occurred in the aftermath of the independence of Bangladesh in 1971, in the form of stranded Biharis who were relocated to Pakistan. Smaller numbers of Bengalis and Burmese immigrants followed suit much later. The Soviet war in Afghanistan in the 1980s forced millions of Afghan refugees into Pakistan, particularly in the northwestern regions. Inevitably, the rapid urbanisation caused by these large population movements has also brought new political and socio-economic complexities.
In addition to immigration, economic events such as the green revolution and political developments, among a host of other factors, are also important causes of urbanisation.