French Guiana (French: Guyane française) was an overseas territory of France located on the northern Atlantic coastline of South America. It shared borders with Brazil to the south and east, and the Netherlands' Surinam to the west. Initially settled as early as 1763, these first efforts were greatly inhibited and ultimately thwarted by tropical disease and climate, with all but a sixth of over 12,000 colonists dying out. For over sixty years, from 1852 to 1916, France operated the controversial Devil's Island (Île du Diable) penal colony/prison nine miles off the coast. In early 1916, following Imperial Brazil's declaration of war against France and its' allies (Austria-Hungary and Imperial Russia), the territory was quickly overrun by the Imperial Brazilian Army, with the territorial capital of Cayenne finally surrendering on May 29. As per the terms set in the Treaty of Amsterdam, French Guiana was formally ceded to Brazil in 1919, and is today a part of the Brazilian province of Amapá.