Complex sentence: The Japanese forces under Kuroda Nagamasa fell back and met up with the main host led by Mori Hidemoto, upon seeing the large host approaching the area, the Ming forces retreated further back towards Seoul again.
Split into simpler sentences: The Japanese forces under Kuroda Nagamasa fell back and met up with the main host led by Mori Hidemoto. Upon seeing the large host approaching the area, the Ming forces retreated further back towards Seoul again.