Yeah, Minas Nova allied with Alara after war was declared. Warchief actually offered to join Xavax against Alara at first (Aramon is part of a council that Selenia presented the letter to), only going the other way after we refused.
As for Aramon's part, you might be surprised to learn that he was vocally against war with Alara from the start, which was one of the reasons he joined the loyalist faction in the rebellion (the rebel faction consisted mostly of nobles in favor of war with Alara, Kellan Dodger and Grathe Geg chief among them, with also Kuriga heavily favoring the rebel faction until Selenia was persuaded to join the loyalists, none of whom he got along with). He ran against Selenia on a pro-Perleone war platform, and he was resistant to the idea of going to war with Alara until Robb stated that Xavax were cowards, which he took to mean the whole realm, and took it as a personal insult. Which is why he offered King Robb a duel to surrender the first time they encountered each other after war was declared. Ironically, had Robb accepted, I was more than prepared to pressure for peace, Robb lost a lot of respect in Aramon's eyes by ignoring the challenge, and even more for the whole rape and genocide bit (which put him on the level of his brother and Outer Tilog, things he absolutely hates). If he comes across as arrogant, part of it is because he views dirt with more respect than he does Robb, and by extension, Alara.
