Complex sentence: The original plan for the Chicago Federal Center called for two towers, the first to house federal agencies including the U.S. Department of the Treasury and U.S. Department of Defense, and the second for the courts, U.S. Department of Justice, and U.S. Postal Service.
Split into simpler sentences: The original plan for the Chicago Federal Center called for two towers. The second was for the courts, U.S. Department of Justice, and U.S. Postal Service.