Crusade Against Christian Neighbours in the Baltic. Boniface IX’s Crusading Bull of 1401 to Queen Margaret I of the Kalmar Union

The Baltic crusades are usually associated with conflicts against the pagan tribes of the region, but an element that is often overlooked is that they also included fellow Christians among their targets. This chapter will analyse the historiography as well as the reasons why these crusades were called and how they were perceived at the time. It will focus in particular on the crusade in support of the Kalmar Union—one of the best examples of crusading against Christians in the region. The Union was established in 1397 and comprised of the three Scandinavian kingdoms and dependencies, stretching from Russia to North America and from Nordkap to Hamburg. In 1401, Pope Boniface IX ordered the archbishops in the provinces of Scandinavia to preach a crusade against the enemies of the Union, “be they Christian or pagan.” This was a highly unusual formulation, but the ecclesiastical and political situation was also extraordinary. The Latin church was divided between two or three popes at the time, and Boniface needed all the help he could get. The bull was issued in response to a request from Queen Margaret, the de facto leader of the Kalmar Union. The Union was disputed from within and it had also inherited numerous external enemies. The Swedes had fought against Orthodox Russians for decades, the Danes had fought against or together with the Teutonic Order, and the Lithuanian-Polish union, established in 1386, had created a Catholic superpower with strong interests in the Baltic. Normally, the popes carefully denounced their enemies as heretics before they declared a crusade against them, but this was not the case in 1401, maybe because the enemies of the Kalmar Union were so many and so well established as Catholics.