It has been pretty thoroughly discussed at Catastrophism that the Younger Dryas was probably caused by asteroid/comet strikes along the Canadian border and perhaps in northern Europe. A well researched book by Firestone, et al. lays out this theory in detail. SC: Give him the reference please.
Once you have checked this out, see how it would affect your theorizing. I am inclined to think that Ice Ages are cause by megavolcanos and large asteroids/comets.
Btw, while I used a 12K year cycle in the description above, my thoughts are that this is a continuous and complex process with super cycles matching the start of ice ages brought on by a massive increase in volcanic activity around the planet, and prior warm periods somehow a part of the cycle.
I know, it all needs a lot more thought/study, but I'm pretty convinced the main mechanism is tidal with the core playing a major role. Of course there are other factors (e.g., impacts, orbits, solar).