The Mormon pioneers were members of the Church of Jesus Christ of Latter-day Saints (LDS Church), also known as Latter Day Saints, who migrated beginning in the mid-1840s until the late-1860s across the United States from the Midwest to the Salt Lake Valley in what is today the U.S. state of Utah. At the time of the planning of the exodus in 1846, the territory was part of the Republic of Mexico, with which the U.S. soon went to war over a border dispute left unresolved after the annexation of Texas. The Salt Lake Valley became American territory as a result of this war.