Many times the Swedish crown was inherited by child kings over the course of the kingdom's existence; consequently, real power was held for long periods by regents (notably those of the Sture family) chosen by the Swedish parliament. King Christian II of Denmark, who asserted his claim to Sweden by force of arms, ordered a massacre of Swedish nobles in Stockholm in 1520. This came to be known as the "Stockholm blood bath" and stirred the Swedish nobility to new resistance and, on 6 June (now Sweden's national holiday) in 1523, they made Gustav Vasa their king. This is sometimes considered as the foundation of modern Sweden. Shortly afterwards the new king rejected Catholicism and led Sweden into the Protestant Reformation.