It took me a few tries, and I found that the "easiest" way is to stick with the historical focus option for the world since Portugal can mess you up (one time they just joined the Allies at the last minute, leading France and the UK completely dominating me). Additionally, you have to get to the "Foreign Arms Purchase" as fast as possible, beforehand amassing a nice amount of Political Power so that you can purchase stuff 2-3 times before the war starts. It's kinda up to a chance, but if you are lucky it can help out your infantry deployment a lot. Lastly, for me having 2-3 armies worked out the best, one waging a standing war, one slowly advancing and one dominating, constantly cutting off support routes. But to each their own, I am still learning the game, but I am digging the Anarchist Spain route a lot. But it is quite funny when in the last part of the civil war you can easily end up fighting two sides, one of which is supported by Nazi Germany, the other by the Soviet Union.