When I studied costume in college, this was one of those thongs that got explained on day one.
Historically, women's fashion was much more complicated up until modern times and they frequently had dressers to assist them. Since the majority of humans are right-handed, button sides developed to play to that. Men, who tended to dress themselves have garments that button on the right. Women, who tended to be dressed by some standing in front of them, facing them, have garments that button on the left...which facilitates a right-handed person doing the dressing.
If you like that then how about the reason for most spiral staircases going in a clockwise direction?
Most people are right handed and most attackers will be trying to go up the staircase which means that their sword arm will be tightly hampered by the centre pole allowing only half hearted swipes at ankles. The defender on the other hand will have his sword arm in plenty of free space enabling him to aim forceful blows to the opponents head.
I'm not really sure where I picked it up, possibly at school but I do have an interest in history. I can't think of a specific book at the moment but I'll have a think.
Probably a book on castles would be the thing, the designs are generally very clever. For example, think of a square or round castle. You are one the battlements, I'm on the ground. If I manage to make the foot of the wall I'm virtually inaccessible to you and can tunnel through at my leisure. If the bottom of the wall is flared out, I'm more vulnerable but still have some protection from you. If however the ground plan is a multi-leaved clover leaf. There is no shelter at all, anywhere. If I try to scale the wall there is no point where you can't put an arrow in my back. If I try to tunnel, you are always behind me.