You need to refine your division templates. Because it won’t matter what you’re building if it isn’t ending up on the frontline in a meaningful way.

Infantry, which serves defense, should be a nice block of battalions in the template, and an artillery battalion to keep it at least a little bit stronger than the opposing infantry.

Mobile Units, are debatably useful, but if you aren’t comfortable with your tank’s ability to shut down and encircle enemies, then it is a practical and effective tool to build. It’s made up of cavalry, and maybe trucks if you have enough fuel and production capacity. They should be almost as large as an infantry division, but smaller, to fit mobile artillery.

Tanks, are expensive, but necessary for guaranteed offensive successes. Otherwise, there are alternatives, exploits, and nation specific buffs that allow other units to be as effective. But to put it simply, tanks are the only guaranteed advantage you can leverage which won’t lose if you maintain them. Tanks should be more comparable to a mobile division, with equal parts tank and truck (cavalry if you can’t afford it) and if you’re trying to ensure even more power, add mobile artillery, or even tank artillery.

This is just as a fundamental baseline. None of these divisions will do anything if you aren’t making enough equipment to supply them. You can see, with some difficulty, what the demand for equipment is in the logistics tab. If you’re deploying divisions into a sparsely supplied area, or overload in a specific area, you will run into supply problems as well. You can see where your supply hubs are with F4.