Final answer:
The initial conflict of the Thirty Years' War was a civil conflict between Catholic and Protestant states within the Holy Roman Empire before it expanded due to interventions by other European powers.
Step-by-step explanation:
The Thirty Years' War was one of the longest and most destructive conflicts in European history, lasting from 1618 to 1648. Fought primarily in Central Europe, an estimated 4.5 to 8 million soldiers and civilians died as a result of battle, famine, and disease, while some areas of modern Germany experienced population declines of over 50%. Related conflicts include the Eighty Years' War, the War of the Mantuan Succession, the Franco-Spanish War, the Mortenson War, the Dutch-Portuguese War and the Portuguese Restoration War.
The initial conflict in the Thirty Years' War was a civil conflict between religious faiths. It began in 1618 within the Holy Roman Empire between Catholic and Protestant states. However, it escalated as other European powers joined the conflict, each seeking to advance its own political and territorial interests. The war was complex and involved many different battles and negotiations, but finally ended with the Peace of Westphalia in 1648, which recognized the sovereignty of the German states and significantly affected the political landscape of Europe.