Second most-populous Protestant denomination
in the United States
The United Methodist Church traces its roots back to John Wesley's Holy Club at Oxford University in the mid-1700s. The word "methodist" was actually a slur against their strict regimen of meetings and prayer. Campus ministers use this origin to passionately defend their ministries from budget cuts -- the catchphrase being, "John Wesley was a campus minister."
Methodism took off when Wesley sent two missionaries to America, Thomas Coke and Francis Asbury. (Wesley himself had gone to Savannah, Georgia early in that colony's development, and gotten himself run out of town for reacting badly when the niece of a local aristocrat rejected him.) Although his original instructions were to go to the local Anglican church for sacraments such as Communion and baptism, the denomination broke free not long after the American Revolution, calling itself the Methodist Episcopal Church ("Episcopal" being a reference to a governing structure involving bishops). Wesley himself was an Anglican priest, and had not seen the need to separate the Methodists from the Anglican Church until this point.
The denomination split in six during the 1800s -- the African Methodist Episcopal Church left in 1816, AME Zion Church in 1821, Methodist Protestant Church in 1830, the remaining church split into Methodist Episcopal Church (North) and Methodist Episcopal Church, South in 1844, and the Colored Methodist Episcopal Church (now Christian Methodist Episcopal Church) broke from the M.E. Church, South in 1870. The three primarily African-American denominations have remained independent to this day.
In April 1939, the M.E. Church, M.E. Church South, and Methodist Protestant Church reunited as The Methodist Church. This set the stage for the final merger in 1968, where The Methodist Church and the Evangelical United Brethren joined to form the United Methodist Church. (Historically, the predecessors of the EUB Church had been very close to Methodist doctrine; the reason the churches were not united from the start was language -- most early Brethren churches in America were German-speaking.)
Aside from typical Protestant teachings, one major focus of Methodism is the concept of grace, as in "It is through grace alone you are saved, by faith." The UMC is fairly middle-of-the-road theologically, although with the usual disconnect between often-liberal leaders and a mostly-conservative laity.