German Medieval Armies 1000-1300. It is an Osprey Book.

I got the following books for christmas:
German Medieval Armies 1000-1300
German Medieval Armies 1300-1500
Swiss at War 1300-1500
Medieval European Armies
Armies of Medieval Russia 750-1250
Medieval Russian Armies 1250-1500

I started with the Medieval European Armies book because it is very general and gave me a sort of introduction to the period.