Complex sentence: What became known as the McMillan Plan was finalized in 1901 and included re-landscaping the Capitol grounds and the National Mall, clearing slums, and establishing a new city-wide park system.
Split into simpler sentences: What became known as the McMillan Plan was finalized in 1901. The plan included re-landscaping the Capitol grounds and the National Mall, clearing slums, and establishing a new city-wide park system.