The first sailors and marines landed in Port-au-Prince on July 28. Within six weeks, representatives from the United States controlled Haitian customs houses and administrative institutions. A few weeks later, the US State Department installs Senator Philippe Sudre Dartiguenave as the head of state. "When the National Assembly met, the Marines stood in the aisles with their bayonets until the man selected by the American Minister was made President," Smedley Butler, a Marine who will administer Haiti's local police force, laters writes.

Under pressure from the United States, Haitian President Sudre Dartiguenave signs, and the Haitian senate ratifies, a treaty legitimizing the US occupation and putting Haitian finances and government under the control of the US for the next 20 years. The act also disbands the Haitian army, creating in its place a single US-led, 3000-man police force known as the Gendarmerie d'Haiti which answers to the US Secretary of State. The Gendarmerie oversees the implementation of a US law reviving the practice of conscripted labor, or corvée, which requires Haitian peasants to work on roads for three days a year. However, in some cases workers are forced to work bound with ropes for weeks and even months. The practice reminds Haitians of their slavery under the French and inspires a rebellion in 1918.

The US drafts a constitution for Haiti, which notably excludes a provision from the country's previous constitution which had prohibited foreign ownership of land. Under the US-drafted constitution, foreign investors would be able to purchase fertile areas and establish sugar cane, cacao, banana, cotton, tobacco, and sisal plantations. But the Haitian legislature finds the US-proposed constitution unacceptable and continues working on a new document which would reverse the terms of the 1915 treaty (see November 11, 1915), giving control of Haiti back to its own government, and which would leave the previous constitution's land restrictions intact. When a copy of the document is sent to Washington, it is quickly rejected by the US State Department which complains that it is "unfriendly" and instructs that its passage be prevented. But the Haitian lawmakers continue their work with plans to quickly ratify the new constitution and then impeach Haitian President Dartiguenave on the basis of the new document's provisions. To prevent its passage, Dartiguenave orders US Marine Smedley Butler to dissolve the Haitian legislature, which he does as they are preparing to vote on the new constitution. Smedley claims that the measure is necessary in order "to end the spirit of anarchy which animates it [the Hatian legislature]."

On June 12, 1918, the US authorities in Haiti submit the US-drafted constitution to a popular referendum, which approves it in a landslide. Less than 5 percent of Haiti's population participate in the vote. And on June 19, 1918, Haiti's new constitution goes into effect. Sudre Dartiguenave remains president, though his position is nothing more than that of a figurehead. Real power remains with the US occupiers.