User blog comment:IamJakuhoRaikoben/Chapter 443: And Then, The Land Was No More, Review./@comment-7418318-20150706191908

Brandish just casually annihilates her subordinates, wipes out the entire island, but leaves potential troublemakers/enemies unharmed?

That really made me wonder if Makarov might have been able to negotiate some kind of treaty with Alvarez and she didn't just casually wipe the FT members out to keep the treaty. Or maybe it was Serena who negotiated the treaty and his joining the Spriggan was one condition? That's be pretty interesting.

Or could it have been her dislike for war that made her spare FT?

Or maybe she just hated Marin and was just looking for a reason to wipe him out. She certainly didn't seem very pleased with him all throughout the chapter.