Complex sentence: The main Japanese force proceeded to Ilocos Norte along the coast, but they also deployed troops to administer the agriculturally-rich Cagayan Valley, facilitating Japanese expropriation of the food supplies.
Split into simpler sentences: The main Japanese force proceeded to Ilocos Norte along the coast. They also deployed troops throughout the Cagayan Valley to administer the agriculturally-rich area to facilitate Japanese expropriation of the food supplies.