[4] Wallenstein and Tilly subsequently gained central and northern Germany, joined their forces during the summer of 1627, invaded Danish Holstein in September, and advanced through the Jutland peninsula[4] as far as Limfjord.

[2] While Christian IV's control of the western Baltic Sea and the Danish isles was unchallenged,[5][6][7] Wallenstein was given the Duchy of Mecklenburg vis-a-vis Denmark in January 1628, and was preparing to construct a navy of his own at the occupied ports of Ålborg, Wismar, Rostock and Greifswald starting in late 1627.

[7] Christian responded with an amphibious campaign in 1628, using his fleet to make landfalls along the occupied coastlines, and destroying the naval facilities in Ålborg, Wismar, and Greifswald.

[7] Wallenstein, who had nevertheless managed to build thirteen vessels in Wismar under Philipp von Mansfeld, was unable to use them, because Swedish ships were blockading that port.

[9] While the Catholic League pressed the emperor to continue the war, and Christian was urged likewise by England and the Netherlands, both sent their emissaries to Lübeck for negotiations in January 1629.

[9] Initially, both sides proposed diametrical peace terms: Christian IV's position was somewhat strengthened by his military successes in 1628, but more so by Wallenstein's fear of a Danish-Swedish alliance.

[14] The treaty restored to Christian his pre-war possessions, and obliged him to cede his claims to Lower Saxon bishoprics, to discontinue his alliances with the North German states, and to not interfere with further imperial affairs in the future.