Complex sentence: The Terminal Tower opened in 1928, two years before the entire Union Terminal complex was complete, and would remain the tallest building in the world outside of New York City until the completion of the Prudential Center in Boston, Massachusetts in 1967.
Split into simpler sentences: The Terminal Tower opened in 1928, two years before the entire Union Terminal complex was complete. It would remain the tallest building in the world outside of New York City until the completion of the Prudential Center in Boston, Massachusetts in 1967.