I mostly operations in defense because I once played as Colombia and the North American Union was invading me, I used one of the defense operations (Elastic Defense) as well as defensive generals, defensive policies, and training. I won the 1st war. After a truce, I was an idiot and got rid of my defenses, the NAU player came back after disconnecting after a while, declared war on me again and won (the reason I disbanded my units was because of costs.) I had the nationalist/fascist ideology, so it didn't work too much. (I was trying to form Gran Colombia.) I got help from other countries (mostly Argentina) and also a Kazakhstan player that had nukes! I technically lost the 2nd war, but the NAU player decided to quit and give my land back. Here is a map of the 1st annexation war (keep in mind I had Panama and Ecuador.)
Red=Colombian Defenses
Blue=NAU Offense
White=NAU Aerial Offense