The Methodist Episcopal Church, South was the so-called "Southern Methodist Church" resulting from the split over the issue of slavery in the Methodist Episcopal Church which had been brewing over several years until it came out into the open at a conference held in Louisville, Kentucky, in 1844. This body maintained its own polity until it reunited with the Methodist Episcopal Church and the Methodist Protestant Church to form the The Methodist Church in 1939, which in turn later (1968) merged with the Evangelical United Brethren Church to form The United Methodist Church. Some more theologically conservative MECS congregations dissenting from the merger formed the Southern Methodist Church in 1940.
The Methodist Episcopal Church, South is most remembered for its reluctance to oppose slavery and its lack of hospitality toward African Americans. However, the church was responsible for founding three of the South's top divinity schools: Vanderbilt Divinity School, Duke University Divinity School, and Candler School of Theology at Emory University. Vanderbilt severed its ties with the denomination in the early 1900s. Duke and Candler maintain a relationship with The United Methodist Church. All three enroll students primarily from mainline Protestant denominations, and all three have a reputation for being progressive.
Err...I have no idea. But I know they're different, LOL!