Kammala jumla mai zuwa: Da'awar Isabella ba ta da tabbaci, tunda aurenta da Ferdinand ya fusata ɗan uwanta Henry IV na Castile kuma ya janye goyon bayansa don ta zama magajinsa wanda aka tsara a cikin Yarjejeniyar Bulls na Guisando. Henry a maimakon haka ya gane Joanna na Castile, wanda aka haifa a lokacin aurensa da Joanna na Portugal, amma wanda mahaifinsa ya kasance a cikin shakka, tun lokacin da aka yi jita-jita cewa Henry ba shi da iko. Lokacin da Henry ya mutu a shekara ta 1474, Isabella ta yi ikirarin da'awarta ga kursiyin, wanda Joanna mai shekaru goma sha uku ya kalubalanci. Joanna ta nemi taimakon mijinta (wanda kuma kawunta ne), Afonso V na Fotigal, don neman kursiyin. Wannan rikici tsakanin masu neman takara ya haifar da
Yaƙin 1475<unk>1479. Isabella ta nemi taimakon Aragon, tare da mijinta, magaji, da mahaifinsa, Juan II na Aragon suna ba da shi. Kodayake Aragon ya ba da goyon baya ga dalilin Isabella, magoya bayan Isabella sun ba da izini, an yarda da Isabella a matsayin magaji na kambi na Castile. Juan II ya mutu a shekara ta 1479, kuma Ferdinand ya gaji kursiyin a Janairu 1479.