This is a great concept. As far as I am aware, this is a new mechanic: new to me at least. When I started playing, I was quickly hooked, and enjoyed discovering the way to play and devising strategies. The problem is that the difficulty has no curve to it. I played for a good while, and the sponsored troops never reached my city. The game is too easy, but to begin with that was fine. I found myself getting bored, though, before there was any risk of losing. Music might hold my attention for longer, but the key is to scale the difficulty over time, to invite some challenge into the experience
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This is a really promising start to what could be a great game. Good work!