This may seem like a very stupid question, but I just started playing Call of Cthulhu so I don't know much aout the rules and stuff yet.
Anyway, in the rulebook that comes with the coreset, it says to put two faction cards together to make one deck. So my question is, when I eventually start to build my own decks from the ground up, do I have to have two factions in it? Can it be more then two or maybe even just have one faction?