Anna, I can recommend two excellent books on shoes by Jonathan Walford (that's Jonathan up there ^).
Shoes from the last twenty years can be quite hard to date as the styles changed rapidly for a lot of it, with influence from all kinds of previous eras. I find it interesting that at the same time shoes became very diverse, general apparel fashion changes really slowed down: not coincidental. I love shoes and although I paid a lot of attention to what was happening, I found that very few of the styles were to my liking - in the mid '90s the Edwardian style with a waisted/Louis heel came in and I love those - wish I'd bought more but of course, I wore them until they fell apart. Since 2000 the shoes have been particularly unpleasant I think. Many heels were uncomfortable to walk in. My least favourite is the kitten heel, that came back in the early '00s.