I think too many people think of factions as opposing armies. They are really on the same side with a different point of view. Political Parties are the best example of factions. I'm not talking about Dems vs GOP but the factions in them. For example the GOP has a libertarian side and a social conservative side and many more but they are more similar than different so that's why they are the same party even though there may be one or two issues that they strongly disagree with each other on. The parties themselves are also factions since they are all Americans and want to have whats best for the country (they are on the same side) but they have very different opinions on what to do. TL;DR Factions are on the same side