sentences:  Lacking the troops and materiel to conduct full-scale conventional warfare, the army's strategies were primarily to form pockets of resistance in occupied areas to harass the Japanese troops and undermine their attempts at local administration, and to launch small surprise attacks to divert resources from Japan's advance into China Proper or against the Soviet Union after the border clashes of Chengkufeng (1938) and Battle of Khalkhin Gol (1939).Yang twice commanded western marches that threatened Japanese lines of communication to Tieling and Fushun in Liaoning Province.From the latter half of 1938, Japan concentrated large numbers of its troops in Manchukuo with the mission of encircling Yang's army and placed a 10,000-yuan bounty on his head.