For much of the High Middle Ages, Scandinavian rulers devoted as much energy to internal disputes as to external expansion. Both Sweden and Norway lapsed into a century of instability in the 1130s. Sweden’s revival began with Birger Jarl Magnusson, regent in the 1240s, who led a crusade into Finland, conquering and converting its southern borderlands. Norway began to restore order under the fittingly named Haakon the Law Mender (1247–63). Denmark’s ‘Period of Decay’ set in just as its northern rivals began to recover, but would also last a century. Earlier, Valdemar the Great (1146–82) had conquered the Rugians, and captured German and Pomeranian territory. His son, Valdemar the Victorious (1202–41), answered a call from the Teutonic Order of the Sword Brothers to a crusade against the pagan Estonians. He won a decisive victory and built the great fortress at Reval.
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