It's not Nexon's job to create an invincible war tactic for poor attackers or those using inferior troops. If you use heavy cavalry (regular tanks), use demolition on silos, don't consider fighters as an offensive priority, ..., then you have much more to fix and an invincible war tactic is not the solution.
Try this:
Are you Industrial Age?
Use 100% cannons, commandos, and shooters in war. And 3 planes. And donated bazookas. Mostly decoys, maybe a sabotage or two, but that's it. Master this.
Are you Global Age?
Maximize your offense (namely, bazookas/heavy tanks/commandos/infantry/cannons/fighters), and offensive buildings (e.g., barracks, war academy, merc camp) and then go Atomic. Do it.
Are you Atomic Age?
Get all the planes, upgrade your aforementioned factory troops, get tank destroyer mercs, get Assault Rally to level 3.
Prioritize offense over defense. Time is precious. This is not a farming game. Assault Rally does not exist to solve your mistakes.