He succeeded his brother Charles XV and IV on 18 September 1872, and was crowned as king of Norway in the Nidaros Cathedral in Trondheim on 18 July 1873. At the accession he adopted as his motto "Brödrafolkens väl" / "Broderfolkenes Vel" ("The Welfare of the Brother Peoples"). While the King and the Royal Court resided mostly in Sweden, Oscar made the effort of learning to be fluent in Norwegian and from the very beginning he realized the essential difficulties in the maintenance of the union between the two countries.