English Civil Wars
The English Civil Wars were a series of wars fought during the mid-17th century that ended up with the establishment of England's first standing army, the decapitation of a monarch and the rise to power of a religious zealot.
Some people put part of the blame for the ECW on the nearly-finished 30 Years War in Europe. Indeed some of the mercenary troops (notably some of the Irish were veterans of that conflict. In many ways it would have been strange for England to not become involved in this massive Catholic vs Protestant conflict that severely depopulated portions of Europe and established what many historians consider to be the era of "modern" warfare.
Sometimes inaccurately refered to as the English Civil War.
Here are some online resources, including reenactment organization's websites: