The focus of the study is the problem of the loyalty of the imperial estates during the Thirty Years' War of 1618—1648. Throughout the history of the Holy Roman Empire, various unions and associations of estates at the regional and interregional level played a very significant role. The factor of state consolidation became especially important in the era of the Reformation and the Thirty Years' War. The Evangelical Union, established in 1608, and the Catholic League, founded in 1609, aimed not so much at opposition to the emperor as at strengthening the imperial organization. It was about protecting the religious and secular peace of 1495 and 1555, the rights of the estates and the so-called “deutsche Libertät”. During the Thirty Years’ War, the Protestant estates of the Empire preferred to act within the legal framework of the Empire. Within the framework of journalistic propaganda and official correspondence, the main target was either individual institutions (the Catholic League), or individuals (Wallenstein, Tilly), or the intrigues of foreign countries (Spain). Actually, the emperor himself never acted as a direct object of criticism. Sweden's intervention in the war did not radically change the principles of relations between the estates and the crown. The leading Protestant principalities, above all Saxony, did not want to openly oppose Emperor Ferdinand. A typical example here was the union of the Protestant estates with Sweden, which was concluded in 1633. Despite the pressure of the Swedish allies, the German estates refused to consider the emperor of the Holy Roman Empire as their enemy. Thus, opportunities were preserved for a final compromise between the emperor and the estates within the framework of the Treaty of Westphalia in 1648.