>>213537812 (OP)
Swedish Vasa died without an heir. Meaning the polish Vasa was meant to inherit the kingdom. Swedish nobility and clergy put up some rando on the throne instead with the demand that he immediatly go kill anyone with claims to their lands. Then all of this went together with the whole split between prosties and catholics etc.
Nearly the exact same backdraw to what caused the 100 year war between France and England