I really enjoy the way this game develops. At first, nobody in in command control and maybe your faction has one army commander. Then as the war advances command begins to allow division formation and a few corps and the rail is brought into control. But also, meanwhile foreign forces intervene, Italy and Germany for the Nationalists and the Soviets and International brigades for the Republic.
I continue to be surprised by new international units. After playing many times, I noticed for the first time an Irish Catholic unit joining the Nationalist side. So much detail in the gathering forces.
Finally, both side develop mature armies insensitive to the times, but only out to assert final domination.