Ohh, I adore this both visually and in concept.
As it stands it kind of suffers from a lack of an end goal, and the fact you can place tiles on the right side of the board makes it very easy to break (I plugged up all the spawns with my own rocks and soldiers- having blue tiles take damage on the last column would probably fix that), but this is a very very solid foundation.
You've absolutely nailed the soft-strategy vibe here and I would love to see it fleshed out into a full game. I can definitely see it having some sort of 'key unit' system - each level could have a General or an Outpost you have to destroy above and beyond the core game loop.
Best of luck, I look forward to seeing you in the review video!