A series of rebellions among the indigenous Liberian population took place between the 1850s and 1920s. In 1854, a newly independent African-American state in the region, the Republic of Maryland, was forced by an insurgency of the Grebo and the Kru people to join Liberia. Liberia's expansion brought the colony into border disputes with the French and British in French Guinea and Sierra Leone, respectively. The presence and protection of the U.S. Navy in West Africa until 1916 ensured that Liberia's territorial acquisitions or independence were never under threat.