It really depends. If you're taking them from the very beginning, a two-line history taking them up to the point you're starting from wouldn't be enough. I would say that it's important to show us that you know the canon, but there's no need to outline the whole thing. If you can thoroughly explain their history before the canon, and give us an idea of where it's going, that's fine.

Also keep in mind that we don't need the history section to be really detailed, and it can be in point form. It doesn't need to be a million pages with all of the minute detail, but a good overview that shows us you know your stuff, and gives us the context we need if we're unfamiliar with the canon, is what we're looking for.