Complex sentence: By 25 February, the Chinese had seized Cam Đường, yet were still struggling to exterminate pockets of Vietnamese resistance in Lào Cai and other towns under their control, a situation which had not ended until 27 February.
Split into simpler sentences: By 25 February, the Chinese had seized Cam Đường. However, Vietnamese resistance in Lào Cai and other towns continued until 27 February.