Without being familiar with the details this sounds as if they bit off more than they could chew (or invaded more than they could hold). Holding territory is wa

Without being familiar with the details this sounds as if they bit off more than they could chew (or invaded more than they could hold). Holding territory is way, way harder than winning it in the first place. If your actions led to your own clan's erradication 30 years after the fact then tour actions might not have been the smartest (unless e.g. your clan was going to be erradicated either way and you managed to buy them time).