The Trịnh–Nguyễn War lasted from 1627 until finally 1672. The Trịnh Military staged at the very least 7 offensives, all of which failed to seize Phú Xuân. For just a time, beginning in 1651, the Nguyễn on their own went over the offensive and attacked parts of Trịnh territory. From https://keeganmwelr.bloguerosa.com/30257916/6623-an-overview