In 1493, King John of Denmark entered into a formal treaty with the grand prince of Muscovy, which was later renewed and discontinued only with the fall of King Christian II. The treaty generated frequent embassies to Copenhagen and Moscow. The treaty was clearly aimed against Sweden and posed a serious strategic problem there. It also provides a backdrop to the diminished Swedish political trust in the Oldenburg kings. Several medieval papal bulls prohibited Latin Christians from contact with infidels and schismatics. This papal embargo represented an over-arching policy that all within the Latin Christian community were expected to observe. The need for trade required degrees of embargo and in effect, the embargo only prohibited trade and interactions with infidels that may harm the Christian community – especially arms trade and offensive alliances. The Danish-Muscovite alliance was a clear breach of this embargo. Earlier studies have not, however, appreciated the significance of this alliance in the larger international context. This article studies the role of Muscovy in the conflicts between Sweden and Denmark from 1493 to 1523. How did the Oldenburg kings utilise the treaty to pursue their strategic goals? What were the Swedish repercussions? Did the Oldenburg kings publicly acknowledge their Muscovite liaison? How did the larger Latin Christian community react? What does this treaty tell us about political change in early sixteenth-century Northern Europe?