Glaciation is most strongly dependent on Milankovich cycles:

  - https://en.wikipedia.org/wiki/Milankovitch_cycles
  - http://www.indiana.edu/~geol105/images/gaia_chapter_4/milankovitch.htm

Plate tectonics and volcanic activity have also influenced climate in the past, e.g. the closing of the Panamanian isthmus, or the formation of the Deccan Traps.

Interestingly, the original paper proposing AGW (in 1896) was actually intended to explain Ice Ages:

  - http://www.rsc.org/images/Arrhenius1896_tcm18-173546.pdf