Involvements Abroad
Relations were hostile with both Sweden and Denmark from the start. During his rivalry with Earl Skule, Skule attempted to gain the support of Valdemar II of Denmark, but any aid was made impossible after Valdemar's capture by one of his vassals. Since the Danes wanted overlordship of Norway and supported the Guelphs (those supporting the Pope over the Holy Roman Emperor), Haakon in turn sought closer ties with the Ghibelline Emperor Frederick II, who sent ambassadors to Norway. As Haakon had gained a powerful reputation due to the strength of his fleet, other European rulers wanted to benefit from his friendship. Despite the struggle between the Pope and the Emperor, Haakon was able to maintain friendships with both. One time, Haakon rejected an offer from the Pope to become Holy Roman Emperor. It has been suggested that Haakon hesitated to leave Norway due to the Mongol threat.
Haakon pursued a foreign policy that was active in all directions (although foremost to the west and south-east). In the north-east, the relationship with Novgorod had been tense due to a dispute over the right to tax the Sami people, as well as raiding from both Norwegian and Karelian sides. Eventually, the Mongol threat drove Prince Alexander Nevsky to negotiations with Haakon that likely strengthened Norwegian control of Troms and Finnmark. An embassy from Novgorod one time asked for Haakon's daughter Christina for a marriage, but Haakon refused due to the Mongol threat. Due to the Elven-based Norwegian presence in the seas around the south of Sweden and into the Baltic Sea, Norway increasingly relied on Baltic grain from Lübeck. The import was however halted in the late 1240s due to the plundering of Norwegian ships in Danish seas by ships from Lübeck. In 1250, Haakon made a peace and trade agreement with Lübeck, which eventually also opened the city of Bergen to the Hanseatic League. During the conflict, Haakon had reportedly been offered control over the city by Holy Roman Emperor Frederick II. In any case, Haakon's policy regarding Northern German ports largely derived from his strategy of attempting to exploit the internal turmoil that had erupted in Denmark following the death of King Valdemar II in 1241.
In Scandinavia, Haakon regularly met with neighbouring rulers in the border-area around Elven from the late 1240s through the 1250s. Using grand fleets as envoys, Haakon's fleet at most reportedly counted over 300 ships. Haakon sought to expand his kingdom southwards of Elven into the Danish province of Halland. He thus looked for alliance with the Swedes, as well as ties with opponents of the ruling line of monarchs of Denmark. Haakon made a deal with Swedish leader Earl Birger in 1249 about a joint Swedish-Norwegian invasion into Halland and Scania, but the agreement was eventually abandoned by the Swedes (see Treaty of Lödöse). Haakon claimed Halland in 1253, and finally invaded the province on his own in 1256, demanding it as compensation for the looting of Norwegian ships in Danish seas. He was however forced to renounce his claims in 1257 after a peace agreement was made with Christopher I of Denmark. Haakon thereafter negotiated a marriage between his only remaining son Magnus and Ingeborg, daughter of former Danish king Eric Ploughpenny. Haakon had also reconciled with the Swedes when he had his son Haakon the Young marry a daughter of Earl Birger. Haakon's Nordic policies initiated the build-up to the later personal unions (called the Kalmar Union), that in the end had dire consequences for Norway as it did not have the economic and military resources to persevere and maintain Haakon's aggressive policies.
More distantly, Haakon sought an alliance with Alfonso X of Castile, a potential next Holy Roman Emperor—chiefly as it would guarantee new supplies of grain in light of rising prices in England, and possibly giving access to Baltic grain through Norwegian control of Lübeck. Alfonso in turn sought to expand his influence in Northern Europe, as well as to gain Norwegian naval assistance for the campaign or crusade he had proposed in Morocco (seeing that the Iberian Moors received backing overseas from North Africa). Haakon could thus potentially also fulfill his papal vow of crusade, although he likely did not intend to. He sent an embassy to Castile in 1255, and the accompanying Castilian ambassador on the return back to Norway proposed to establish the "strongest ties of friendship" with Haakon. At the request of Alfonso, Haakon gave his consent that his daughter Christina could go to Castile and marry one of Alfonso's brothers. Christina's death four years after the childless marriage, however, marked an effective end of the short-lived "alliance", and the proposed crusade fell into the blue.
Read more about this topic: Haakon IV Of Norway, Reign