Actually, there's a good chance they'll never need to fight those others. Miria's whole reason for bringing up that land was to prove that they could safely eliminate the organization without Yoma running rampant across the land. Because, since the Yoma are creations of the organization, eliminate the organization and you eliminate the Yoma threat as well.
That other continent is so far away that no ship leaving port on their continent has ever found it. Frankly, I don't think it matters to Miria which side wins the wars there, just as long as the continent *she* lives on is freed of the hold of the organization, so that more girls don't have to go through what those warriors called Claymores have been through.