PBS Eons has a great video about climate cycles and what caused ebb and flow of the ice ages.  Milankovitch cycles are front and center, with good explanation of how we are affecting the climate today.

Throughout the Pleistocene Epoch, the range of the woolly rhino grew and shrank in sync with global climate. So what caused the climate — and the range of the woolly rhino — to cycle back and forth between such extremes?