 A protracted struggle with the supporters of Euthymios followed, which did not end until the new Emperor Romanos I Lekapenos promulgated the "Tomos of Union" in 920.In the meantime Alexander had died in 913 after provoking a war with Bulgaria, and the underage Constantine VII succeeded to the throne.Nicholas Mystikos became the leading member of the seven-man regency for the young emperor, and as such had to face the advance of Simeon I of Bulgaria on Constantinople.