Qin attacked the town of Qinyang in the State of Han in 265 BC, which made Shangdang (in modern-day southeastern Shanxi province) an exclave land. Qin continued to invade Han in order to occupy Shangdang, which was in a strategic position west of Zhao and its capture would open an invasion route into Zhao. Within four years the Qin army isolated Shangdang from the rest of Han by capturing the main roads and fortresses across the Taihang Mountains. Shangdang was poised to fall.