The Holy Roman Empire was a loose confederation of thousands of semi-autonomous states that represented the political reality of central Europe for almost a millennium. According to the long-standing scholarly assumption, the Empire was weak and ineffective because it was not a centralized kingdom such as France or England. More recently, scholars have sought to examine the Empire on its own terms. My own research assesses the Holy Roman Empire’s strengths and limitations in the face of a foreign crisis: the struggle between Denmark and Sweden for hegemony in the Baltic Sea region. The conflict between Sweden and Denmark threatened the fragile religious peace in the Empire as well as the economy of northern German territories. My research has revealed that, contrary to commonly held assumptions, the Empire’s confederal structure provided effective means for defending the Empire’s internal order against external dangers. The Empire, however, was largely incapable of projecting power beyond its borders. These limitations stemmed from the Empire’s internal structure: that of a confederation with elements resembling a modern collective-security organization, or, as some commentators have perceived it, “a community of justice and peace.”