In 1545, Nguyễn Kim was assassinated by an agent of the Mạc. Trịnh Kiểm took this opportunity to assert control over the Nguyễn-Trịnh army. The Trịnh captured more and more of Vietnam from 1545 onwards (nominally fighting on behalf of a new Lê Emperor). Kim had two sons. The younger, Nguyễn Hoàng, was put in charge of new southern provinces of Vietnam in the year 1558. He was to rule the southern lands for the next 55 years and his descendants ruled them for the next 150 years.