The Thirty Years' War consisted of a series of declared and undeclared wars which through the years 1618-1648. It was one of the most destructive European conflicts in history, taking place mostly in Germanic states. Its origins and aims are unclear, and no one cause can be named (some conflicts lasted so long that there remained nobody who remembered the initial reason for the conflict). Historical research suggests that the war began as a religious struggle between Protestants and the Holy Roman Empire (Catholics). It later became a rivalry amongst European powers concerning territory, trade, and power, and vastly changed the political map of Europe as well as its main powers.