Complex sentence: Lithuanian Commonwealth and Sweden traces its roots to the War against Sigismund, where Sigismund III Vasa, at one time king of both the Commonwealth and Sweden, lost the throne of Sweden during the civil war (1597--1599).
Split into simpler sentences: Lithuanian Commonwealth and Sweden traces its roots to the War against Sigismund. In this war, Sigismund III Vasa, at one time king of both the Commonwealth and Sweden, lost the throne of Sweden during the civil war (1597--1599).