What was the primary cause of the Thirty Years' War?

The primary cause of the Thirty Years' War was religious conflict, specifically the struggle between Protestant and Catholic states within the Holy Roman Empire. The war began in 1618 as tensions escalated over religious freedoms and political power, particularly after the Protestant Reformation had fractured the Christian church and created significant divisions in Europe. This religious animosity was exacerbated by the rivalry between major powers, leading to a culmination of conflicts that drew in various states and ultimately expanded into a broader European struggle.

While factors like territorial expansion, political alliances, and colonial competition played roles in the larger context of European conflicts during this period, they were not the fundamental drivers of the Thirty Years' War itself. This conflict was primarily rooted in the deep-seated religious divisions that had emerged in the previous century.