For the next 300 years, the Barbary pirates remained a formidable power in the Mediterranean, but their dominion finally came to an end. During the early 1800s, the United States launched two major naval and land campaigns against Algiers, Tunis, and Tripoli that effectively ended the harassment of shipping and piracy by the Barbary pirates. Aided by the English and the Dutch, the city-states of the Barbary Coast were bombarded into submission, and the practice of capturing and enslaving Christians was brought to an end. Algiers would become a French colony in 1831, and Tunis followed in 1881. Tripoli became an Italian colony in 1911, and Europeans would hold power in North Africa until the middle of the 1900s.