Complex sentence: Sinclair was the Danish King's envoy in Britain a number of times between 1606 and 1621, managing to influence James VI in adopting a more pro-Danish, and less pro-Swedish, stance.
Split into simpler sentences: Sinclair was the Danish King's envoy in Britain a number of times between 1606 and 1621. He managed to influence James VI to adopt a more pro-Danish, and less pro-Swedish, stance.