The country Sweden was founded in 1397. During the early middle ages, Sweden expanded to take over Norrland and Finland and modern Sweden started out of the Kalmar Union formed in 1397. It was the unification of the country by King Gustav Vasa in the 16th century. If you didn't know, Sweden first started as a Scandinavian country in Northern Europe. The name Sweden is derived through back-formation from Old English Swēoþēod, wich meant, " people of the Swedes"