Ok with this flavor the great general idea really makes sense. The question is: How many defeated unit do you want to enable the War Machine? Because the problem is: If it comes to early noone can beat it. 19 strength 3 movement is nothing you should get as early. Even if it's 100-150 units I wouldn't have a problem to get it very very fast before anyone has the chance to defend against it. We all know how many useless units the AI builds...

), but rather than extra gold from combat, I removed unit maintenance, and added a slight healing bonus. Lets you have a massive horde, living off the land, so long as you stay in combat.... Only lasts 5 turns.