Hello, in this tutorial I will explain you how to win Spanish Civil War as Republican Spain(it work at regular difficulty and ironman so you can receive achievement).
At start we have complete Spain, first transfer your forces on east coast then build some military factories at east coast, maybe build some forts but i do not recommended this without air domination. Remember that you must produce only infantry equipment, maybe 1 factory for support equipment.
After 16.02.1936 we can have an event named Civil War that start a war between Nationalist and Republican (Communist) Spain. In the beginning we have a little less army(you will have volunteers from Soviet Union, they will have volunteers from Italy and German Reich), so we must stay defensive at borders - this is important.
We must leave Navarra, Basque Country and Cantabria - encircled place on the north of Spain. You must build our industry so take national focuses on military factories, later take civilian factories and infrastructure. You will need 300 political power for 2 demagogue - Army Defence, Infantry and 300 political power for Conscription Law named Extensive Conscription (5%).
Stay defensively until they manpower will be over, you will have more manpower than him and more equipment so you can build 10 or 15 divisions which have 10 stretch, without support eqiupment. If they manpower will be over, you must push a lot on south to enciclement south and north of their teritories, they will have low equipment so it will be easy.
At the end they will have 1mln loses in manpower, you will have half of this. So do this, good luck and have fun!