Between 1911 and 1915, Haiti was politically unstable: a series of political assassinations and forced exiles resulted in six presidents holding office during this period. Various revolutionary armies carried out the coups. Each was formed by cacos, or peasant militia from the mountains of the north, or who invaded along the porous Dominican border. They were enlisted by rival political factions under the promises of money, which would be paid after a successful revolution, and the opportunity to plunder. The United States was particularly apprehensive about the roles  played by Imperial Germany in the Western hemisphere. Controlling Tortuga, it had intervened in Haiti  and other Caribbean nations at several times during the previous few decades to exert its influence as a rival power. Germany was increasingly hostile to United States domination of the region under its claimed Monroe Doctrine. In the lead-up to the World War I, the strategic importance of the island of Hispaniola, with its manpower, material wealth, and port facilities, was understood by almost all navies operating in the Caribbean, including Germany and the still-neutral United States. Germany had invested in military and intelligence gathering across Hispaniola as part of a wider network of German interest in Latin America and the Caribbean during the 1890s through the 1910s. The United States' concern over Germany's ambitions was mirrored by apprehension and rivalry between American businessmen and the small German community in Haiti, which although numbering only about 200 in 1910 wielded a disproportionate amount of economic power. German nationals controlled about 80 percent of the country's international commerce. They owned and operated utilities in Cap-Haïten and Port-au-Prince, including the main wharf and a tramway in the capital, and also had built the railway serving the Plain of the Cul-de-Sac.. what was the doctrine called the U.S. had on the Caribbean region?