Complex sentence: In the 1st expedition, his efforts were undermined by the lose of Jieting, a passageway into Hanzhong, due to the defiance of Ma Su to listen to the Prime Minister's orders to barricade the pathway.
Split into simpler sentences: In the 1st expedition, his efforts were undermined by the loss of Jieting, a passageway into Hanzhong. This was due to the defiance of Ma Su, who refused to listen to the Prime Minister's orders to barricade the pathway.