Complex sentence: On January 12,1847, after moving to Washington, DC, Schoolcraft married again, at age 53, to Mary Howard (died March 12,1878), a southern slaveholder from an elite planter family of the Beaufort district of South Carolina.
Split into simpler sentences: On January 12,1847, after moving to Washington, DC, Schoolcraft married again, at age 53, to Mary Howard (died March 12,1878). She was a southerner and slaveholder, from an elite planter family of the Beaufort district of South Carolina.