Cluemaster was assassinated by the Court of Owls, setting off that conflict.
- Jason's comments imply that not only was Arthur Brown one of the first to discover the existence of the Court of Owls, but that he was later killed to keep the secret, no doubt due to his gambit to bring down Batman failing. So, it's not too big a leap to assume that his suspicious death leads to an investigation that causes the Batfam to uncover the Court of Owl and sparking the following war.
- Additionally since this war killed both Kate and Renee, it's not too much of a stretch that Steph became Batwoman soon after, finally free of her father for good.
