Alliance Purpose

!I'm more than halfway through this book and struggling to understand the purpose of allying with the neighboring islands. If their people can't utilize magic and are essentially limited to melee combat, how are they supposed to contribute against the venin? We already know from the first book that venin can take down multiple riders at once and command wyverns capable of fire attacks, so what exactly do numbers alone bring to that fight. None of the islanders have dragons (as far as i know yet) so they would easily be useless cannon fodder. Unless they explain it further down in the book, it seems really pointless to go through all of this alliance with these annoying neighbors.!<

!If it does explain later in the book, then say no more and just tell me to "keep reading", but to me this book so far has been kind of "meh" in terms of the believability of everything so far.!<