Ostensibly a religious war with the Protestant Union fighting the Catholic League but with the significant complexities of states seeking to enlarge their territory and/or influence. The development of national identiies was both a contributory factor and an outcome. France for example although Catholic entered on the Protestant side following her traditional enmity with the Hapsburgs. States came in and out of conflict during the course of the thirty years.
The war is often described as having three phases the first from 1618 to 1629, the second from 1630 to 1639 and the third from 1640 to 1648.

• Swedish War 1630 - 1635
• Rocroi 18 May 1643 - 19 May 1643