The Danes secured control over the southern Virgin Islands of Saint Thomas, Saint John, and Saint Croix during the 17th and early 18th centuries. Sugarcane, produced by African slave labor, drove the islands' economy during the 18th and early 19th centuries. In 1917, the US purchased the Danish holdings, which had been in economic decline since the abolition of slavery in 1848. On 6 September 2017, Hurricane Irma passed over the northern Virgin Islands of Saint Thomas and Saint John and inflicted severe damage to structures, roads, the airport on Saint Thomas, communications, and electricity. Less than two weeks later, Hurricane Maria passed over the island of Saint Croix in the southern Virgin Islands, inflicting considerable damage with heavy winds and flooding rains.