Cavalry in World War 1; Transcaucasia

For about a year now I have been following a historical series on YouTube. It's called The Great War, and its gimmick is to follow the events of each week, a hundred years later. It also includes "special," that is topical, episodes. It's really quite good, and can be found here.
I have learned quite a bit from this series.
First, I have always been under the impression that cavalry in WWI was used in the margins of the conflict. Mentions of cavalry have been in the style: "Do you know that the [whatever in whenever] were still using cavalry in WWI? [smirk, smirk]," as if they were just too dumb to think of tanks. But I have learned from the Great War that this is entirely the wrong way of looking at cavalry. Everybody had cavalry; in fact they didn't have enough. Second, the war in Transcaucasia (Georgia, Armenia, Azerbaijan, etc.) was BIG!