Karachi
Predicted increase in population by 2025: 5.6 million
Pakistan's bustling financial and commercial hub was rated by the World Bank as the most business-friendly city in the country, thanks to the low cost of living and setting up shop in the city. International corporations have flooded the city and now account for more than half of the nation's revenue. Aside from expats, Karachi has also seen an influx of migrants, often refugees from Afghanistan, Bangladesh and India, as well as Pakistanis moving from other parts of the country in search of jobs. While the immigrant population has added to the city's culture, it has also contributed to ethnic tension and rivalries, which at times have erupted into deadly violence. High pollution from outdated modes of transportation is becoming a growing problem, as well as the lack of regulation over land use. Karachi must make strides to control its rapid, unchecked construction and is attempting to procure funding to update its metro system that was shut down in 1999 because of constant disrepair. Looking forward, Karachi is planning an environment-enhancing initiative to create parks and more green space within the city.