Complex sentence: The Lost Cause is a set of beliefs common in the white American South in the late 19th and early 20th century that the Confederate cause as a heroic one against great odds despite its defeat.
Split into simpler sentences: The Lost Cause is a set of beliefs common in the white American South in the late 19th and early 20th century. The beliefs portray the Confederate cause as a heroic one against great odds despite its defeat.