Complex sentence: After completion of the contract, from his office in Harrisburg, Pennsylvania, he opened a second office, which, often employing local labor to fulfill international contracts has since been involved in designing and building highways, railroads, bridges, and airfields in 120 countries.
Split into simpler sentences: After completion of the contract he opened a second office which, often employed local labor to fulfill international contracts. He was involved in designing and building highways, railroads, bridges, and airfields in 120 countries.