In 1319 the infant Magnus Eriksson was crowned as king of both Sweden and Norway (which included Iceland and Greenland).
Magnus Eriksson would later on buy Skåneland from Denmark twice first time in 1332 and second time in 1341.The union of these two countries lasted until 1343 when Magnus preemptively let his son Haakon, succeed him to the Norwegian throne, though he would still rule as regent during his son's minority, which ended in 1355, when Haakon came of age.
After only a few decades the relationship between Sweden and the leading power Denmark had deteriorated into open conflict.
Frederick I of Sweden had acceded to the Swedish throne when his wife, Ulrike Eleonora, abdicated in his favour in 1721.
In 1730 he was also in line of succession to the duchy of Hesse-Kassel, which resulted in a personal union that lasted until his death in 1751.