Although sighted by Christopher COLUMBUS in 1493 and claimed for Spain, it was the Dutch who occupied the island in 1631 and set about exploiting its salt deposits. The Spanish retook the island in 1633, but continued to be harassed by the Dutch. The Spanish finally relinquished Saint Martin to the French and Dutch, who divided it amongst themselves in 1648. Friction between the two sides caused the border to frequently fluctuate over the next two centuries, with the French eventually holding the greater portion of the island (about 57%). The cultivation of sugar cane introduced slavery to the island in the late 18th century; the practice was not abolished until 1848. The island became a free port in 1939; the tourism industry was dramatically expanded during the 1970s and 1980s. In 2003, the populace of Saint Martin voted to secede from Guadeloupe and in 2007, the northern portion of the island became a French overseas collectivity.