Military Docterine

Countries prepared their military for war in their own way.  Some focused on their infantry, and others focused on machine power like tanks and airplanes.  In some cases they had their infantry work with their machine power.  Depending on their tactics each country had their advantages.  Especially in the beginning of the war, their tactics helped determine how successful they were.  My question would be how much did each country look at their opponents tactics to help improve their own?