In May, 1560, a war commenced with Denmark which, with several intermissions, lasted for seven years. It has been called The Seven Years’ War of the North. About the same time that Eric became king of Sweden, the young ambitious Frederic II. ascended the throne of Denmark. In the days of Gustavus I., Christian III. had appropriated the Swedish emblem of three crowns for the Danish seal of state, as if by this proclaiming that the Union was considered still extant or that it could be re-established at the opportune moment. King Gustavus had protested, but with no result. When King Frederic kept up the irritating fact of preserving the Swedish emblem, King Eric answered by placing the emblems of Denmark and Norway in the Swedish seal of state. This made things worse and served as a nominal cause for war. The principal interest at stake was the supremacy in the Baltic provinces. The diocese of Œsel, which had accepted a Danish protectorate, was governed by a brother of the Danish king, who had entered into an alliance with Poland against Sweden, Denmark also joining it.
In May, 1563, a Swedish fleet, commanded by Jacob Bagge, left Sweden to bring Princess Christine of Hesse, the promised bride of King Eric. A Danish fleet met them, at the island of Bornholm, and greeted the Swedish ships with some shots from their sharply loaded cannon. The Swedes returned the fire and a naval battle followed, which ended in a defeat for the Danes, who lost their flagship. When Jacob Bagge arrived in Rostock, where he was to meet the princess, her father was found unwilling to let her sail on account of the insecurity brought about by the commencing naval hostilities. This would under ordinary circumstances have enraged the vain and sensitive king, but Eric forgot his rage in his delight at the naval victory. Jacob Bagge was rewarded with a triumphal entry into Stockholm upon his return. He entered the city on foot with a golden chain round his neck, followed by his sub-commanders and surrounded by the banners taken during the battle. The prisoners followed, in chains and with shaved heads. The king’s fool was dancing in front of them, playing on his fiddle. A Danish herald soon afterward reached Stockholm, declaring war with great pomp and ceremony on behalf of his royal master. The city of Lubeck sent a messenger to Stockholm on a similar errand, but was not received by the king. “Since he is sent by the mayor and council of his town and other similar lard-mongers, let him be heard and answered by the mayor and council of Stockholm,” was the royal order.