If in world we have 2 (or more) popes any independent ruler should can select "Which Pope do we accepted?". This can lead to division of catholic world on 2 (and more) more parts and few new diplomatic, interesting situations (eg. ending alliance or friendship due to the conflict about popes/antipopes) and real great schism in west world.
Next element of this would be - join to war in defence/installation "true pope". In extremal situation this can lead to great, european, religious total war before Thirty Years War
Next element of this would be - join to war in defence/installation "true pope". In extremal situation this can lead to great, european, religious total war before Thirty Years War
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