Additionally, the entry of several states into the Union was delayed due to distinctive complicating factors. Among them, Michigan Territory, which petitioned Congress for statehood in 1835, was not admitted to the Union until 1837, due to a boundary dispute with the adjoining state of Ohio. The Republic of Texas requested annexation to the United States in 1837, but fears about potential conflict with Mexico delayed the admission of Texas for nine years. Statehood for Kansas Territory was held up for several years (1854–61) due to a series of internal violent conflicts involving anti-slavery and pro-slavery factions. West Virginia's bid for statehood was also delayed over slavery, and was settled when it agreed to adopt a gradual abolition plan.