Ever played a game which constantly sends a Neverending army of increasingly strong enemies at you? You push back the enemy, establish a fortification, make yourself stronger while those at the front keep the hordes at bay. Then take a bunch of the stronger units you made in the base with the resources of all your territories combined, and send the forth to push back a bit more, repeating the process again and again until the whole map is claimed and optimally fortified. If a territory is overwhelmed, you send fortifications to keep them from claiming more that just that part, and hold the off until you can push forth, not just to reclaim what you lost, but take a bit more territory from them. It's like what the English did to conquer Scotland and Wales, push a bit, then focus on holfingbthe line while you fortify the little territory you gained, then push a bit harder, take more territory, and fortify that as well. Go like a turtle, with a slow advance covered by an impenetrable defense, let them wear themselves out as you slowly take from them, little by little, and give nothing back.