Its difficult for newer players to see beyond war/military. Its a bad choice to build military above whats need to to aquire a c3.You only need a minimum number of certain types of weapons to do this.
Concentrating on your countries economy is paramount to being able to sustain a military.
look around at what corps some of the top 10 ppl on your world are building, lower taxes to 0 and invite ceo's to build.
Follow the countries needs, to level up and reap the coin rewards.Add pop slowly upto 50-60m.
Use scarlets "church of simcountry"guide to start you in the right direction. For the ones that are looking for something more indepth on profits, read wilds leaving guide.
Make income and profit your main target, war will follow.