Right now the game is lacking some very much needed battle mechanics that would improve it. There is a long way to go to make Drug Wars awesome, but here are some points to get there faster.
There should be an option to hide your units in safe houses like you can hide your resources, right now it is crazy to invest in units because very quickly they will all be wiped out, there should be a mechanic to hide your units from attacks. In my example it took me two weeks to get to 4k attack and 3k defense, I woke up and everything was wiped out while I was sleeping.
That is a very dumb game mechanic that needs to change asap. Players should be able to build up their units safely and make that sweet sweet revenge when they wish to (@kevinli be ready). Specially because units cost real life money and there are no mechanics to protect them in any way.
Level Up Rewards
Leveling up your account is the second thing that should give rewards to players in line with raids, rewards like attack or defense boosts, extra resources or resource production boosts that can last for a day, free building upgrade or reduced cost for building upgrades. You know, reward players with something juicy that will urge them to continuously level up.
Make it impossible to send your army to attack your alt accounts or to ask a friend to send one unit to activate the shield. I know this one will be tough to implement, but the battle system can be exploited so easily this way. One solution is to scrap the protection shield and implement safe houses for units like I mentioned before, of course safe houses should cost large amount of resources. Players should be able to pick an active defense or store their units in safe houses where they can get high from their own supply.
All these changes shouldn't be hard to implement but in my opinion would improve the game drastically. Your move devs.