Replayed Civ 2 for the first time in ages (mostly play Alpha Centauri and newer Civs). I keep having situations where I lose an entire army to a single city, or something like six tanks to a musketeer or something. Cannons etc usually also get killed when fighting same-era units. Bombers give unhappiness even when they are in the city. And the maps are usually very large for an eight civ cap. And all of the AI hate you as soon as you're large.
So how do you properly warmonger in this game?
There are a lot of different questions in there. I also began paying Civ2 again after decades of not playing it since it originally came out. I assume you are playing MGE not ToT.
There is a flaw with the AI in the vanilla game. Look for the no hostility patch called attitude.exe. It makes the game playable.
There's a patch called Civ Unlimited. It acts as the boot for the game and it allows enormous maps, enormous numbers of units, money, etc. You need that too.
It is way better to download a scenario than play the vanilla game due to peculiarities. I was working on a mod for the vanilla game which replaced the basic graphics and filled up the empty unit slots. Maybe I'll finish it.
In many scenarios, there are airbases and army fortifications where the units are nearby so that they can be redeployed as needed rather than within a city. You might like some of the modern scenarios at the Scenario League wiki.
New World Order 1.2 is a lot of fun.
http://sleague.civfanatics.com/index.php?title=Category:Atomic
Not only do city walls offer defenses but wonders and improvements and TERRAIN. The base tile that the city was founded upon could offer defensible attributes just as in history.
Chances are high you will end up looking at the unit stats and start tweaking them as the above sort of situation makes it ridiculous where better military units might have difficulty with inferior defenders.
On top of which, there are bonuses based upon the AI level. If you're playing at some high level,then additional defensive bonuses might be layered on top of the situation.
The most boring way to play is to start in 4,000 BC with a single settler as the pace is glacial. If starting back from that point to present day, I suggest a huge map like the Gigamap in the download section. Then create at least ten cities for each civilization. Then give each civilization 1,000 gold. Then start. Then there is enough distance between each and time to build up infrastructure and more cities and units. That game is quite fun with battles in every age.