The occupation creates the constabulary that will choose Haiti's presidents

The United States Marine Corps landed in Haiti in 1915 and stayed nineteen years. President Wilson appears to have feared growing German influence, with Mole Saint Nicolas sitting opposite Guantanamo. American investment in the country was small at the time. Just before the landing, President Vilbrun Guillaume Sam was killed by a crowd and his torn limbs carried through the streets of the capital. It took four years to pacify the country, which required putting down the rising led by Charlemagne Peralte. The Americans then did in Haiti what they had done in Cuba, Nicaragua and the Dominican Republic and created a modern constabulary combining army and police under Marine supervision, the Gendarmerie d'Haiti. It became the Forces Armees d'Haiti and from the late 1930s decided how long any sitting president would remain. Elections and plebiscites held up to 1929 were all controlled by the Marines.

Colonel Littleton Waller took the north in hand. He paid off the Haitian garrison at Ouanaminthe, most of whom claimed the rank of brigadier general at the pay table, and put a Marine company on the Dominican border in their place. More companies went into Grande Rivière du Nord and Fort Liberté, giving him a triangle of garrisons to patrol from. Butler took forty men to locate the Caco strongholds, crossing country no foreigner had entered since the French, and afterwards said Haiti looked like a crumpled sheet of paper. On the afternoon of 24 October 1915 he came within sight of Fort Capois, a cone of rock a thousand feet above him ringed with stone walls and trenches, seven miles south of Saint Suzanne. He turned back toward Grande Rivière and spent the night surrounded and under fire from 400 Cacos. From 1 November the Marines swept west from the Dominican frontier, taking the strongholds one after another, nearly all of them old French forts. The last was Fort Rivière, on the peak of the Montagne Noire, 4,000 feet up.

Holding an army in the north was costing the Haitian government 140,000 gourdes a week and producing nothing. Recruiters were again pulling old men and boys out of village huts, clubbing them and roping them together for the march to the barracks. The fighting had stalled and Rosalvo Bobo was losing his hold on his Cacos, who told him they could walk east over the bridge into the mountains and find another leader whenever they liked. To make the point they beheaded two men of Cap Haitien who had not been enthusiastic enough, and shot others. Consul Livingston watched the heads carried about the streets and called it the worst savagery he had seen in seventeen years there. Bobo was a doctor educated in Paris and campaigning as a progressive. When he reproached a Caco general, the man answered that the Angels had ordered the killings and that if there had been a hundred people he would have killed all of them. The French cruiser Descartes landed marines to guard the consulates.

Dartiguenave's south stayed quiet. The north, the northwest and the Artibonite did not. In early August the American consul Livingston reported Caco bands burning plantations and killing peasants, and said nobody believed they would give up their weapons. The American plan was to buy the fighters out, 100 gourdes for a chief with his gun and 15 gourdes for an ordinary man with his, then defeat whoever remained. Gonaïves came first. Rameau cut the town's water and laid siege with 400 men. Major Smedley Butler arrived by gunboat with orders to break the siege, restore the water and reopen the railway from Ennery. He caught Rameau and 500 Cacos at Poteaux on 20 September. Rameau agreed to talk, denied writing the handbills issued over his name on the truthful ground that he could not read them, and asked whether a portfolio in the new government might be found for him. Five days later he was captured and jailed. That same day, 26 September, Cacos in the red scarves of Ogoun ambushed a Marine platoon at Haut du Cap and killed two men.