In the 21st century, Paris added new museums and a new concert hall, but in 2005 it also experienced violent unrest in the housing projects in the surrounding banlieues (suburbs), inhabited largely by first and second generation immigrants from France's former colonies in the Maghreb and Sub-Saharan Africa. In 2015, the city and the nation were shocked by two deadly terrorist attacks carried out by Islamic extremists. The population of the city declined steadily from 1921 until 2004, due to a decrease in family size and an exodus of the middle class to the suburbs; but it is increasing slowly once again, as young people and immigrants move into the city.