In this paper, we deal with the theme of the war which left its mark on all fields of human activity during the 17th century and later. The war that lasted from 1618 to 1648 was the first total war on European soil, and because of the time frame in which it took place it is called the Thirty Years' War. This name actually denotes a series of international armed conflicts in the wider area of the Holy Roman Empire in the first half of the 17th century. Although often portrayed as a classic religious conflict, the Thirty Years’ War was much more than that. The long-suppressed mutual hatred and intolerance of the great European ruling houses had finally come to light. Although the cause and the initial conflict arose due to religious diversity, the causes were, as always, much more complex. The weakening of feudalism and thus the emergence of the first capitalist relations further burdened a large number of European countries. After hundreds of years of religious unity in European countries, things are forever changed with the appearance of Martin Luther. The most pronounced division into Protestants and Catholics took place in the area of Germany, where a large-scale war would rage ten years later. The war itself begins with a phase that is most often called the Bohemian Revolt. The defenestration in Prague, in which the Czech classes revolted and removed the regents, led to the inevitable beginning of the conflict. The king sent an army to quell the rebellion, but it was soon defeated and forced to withdraw, and the conflicting parties remained in a stalemate. The struggle for power in the Czech lands was of crucial importance to both sides primarily because in the Empire, three of the Dukes electors were Protestants and three were Catholics. The faith of the Czech king, as the seventh Duke elector, would prevail. After some time, however, the imperial army managed to defeat the insurgents and Ferdinand was elected emperor in Frankfurt. The Danish Phase of the war continued in the same tone. The Protestant Danish King Christian IV crosses the northern borders of the empire with support from England and the Netherlands, however Count Tilly and General Wallenstein first separately and then jointly inflict a heavy defeat on the Danes. The war was soon joined by Sweden, which also sided with the reformists and seriously threatened imperial power. Gustav II Adolf chose his battles carefully, often inflicting heavy defeats on the imperial army (especially the one led by Count Tilly). In most battles the Swedish coalition claimed victories, however at Nördlingen, they suffered a heavy defeat with which they were forced to leave southern Germany. The following year, the Heilbronn League disintegrated, after which the force that had been fighting from the shadows until now was directly involved. France had long been watching the Habsburg ruling house with disdain. Although it was a predominantly Catholic country, France joined the Protestant side primarily because of its rivalry with the Holy Roman Empire and Spain. Cardinal Richelieu was the prime minister of King Louis XIII, and made all the important foreign policy decisions on behalf of the emperor. After a series of conflicts, mostly with Spain, which at one point threatened even Paris itself, there were no major territorial changes. After the deaths of Richelieu and Louis XIII, the new government was trying to achieve peace. Finally, it was reached in 1648 and was negotiated in Münster and Osnabrück. it is remembered as the Peace of Westphalia. The consequences of the Thirty Years' War were terrible, unprecedented for the population until then, and it took society a long time to recover.