How about an option in new games to set a Maximum # of Armies on the board? For example, you could set it to 100, and when there are a hundred armies on the board, you can't get any more until some of them get wiped out. If you had armies coming to you but the limit was already reached, your new armies keep getting carried over until you can legally deploy them on one of your turns when the total army population on the board dips below the threshold.
I was inspired by another post on this forum, and a game I played a few times years ago....
There's a board-game where you control one of the various late-bronze-age or early-iron-age powers of the Mediterranean -- IIRC the Greeks, Romans, Carthageneans, Macedonians, Etruscans, Egyptians, etc.... (BTW, you would also get a General or "Caeser", as it's called in the game, which could accompany your troops for a bonus on rolls, but if you lost your "Caeser", you lost the game.) You could buy troops, chariots and triremes from the market.
As more and more troops were fielded, the supply of troops in the box would dwindle, and the price for new troops would escalate, until you couldn't buy any. The only way for the "market" to get "new" troops was to remove troops from the board back into the box -- in other words, loosing them in battle.
I've seen Risk games with ungodly numbers of troops on the board, and it could be argued that such high numbers could not possibly be manned or supported.