Complex sentence: The States' Rights Democratic Party (a.k.a. Dixiecrat Party) was a segregationist, splinter party of the Democratic Party in the mid- 20th century determined to protect what they saw as the Southern way of life against an oppressive federal government.
Split into simpler sentences: The States' Rights Democratic Party (commonly known as the Dixiecrats) was a segregationist political party in the United States. It split with the Democratic Party in the mid- 20th century determined to protect what they saw as the Southern way of life against an oppressive federal government.