I can only add that in my playthrough, at some point, after I became strong enough, I stopped buying units, and when a gray player appeared, I would buy units and drive him away. The gray player has a limited number of heroes, and if you drive all his heroes to the northeast or northwest, he will retreat, he won't be able to buy new ones, and the invasion of the gray player will stop. All that remains is to periodically drive away the green players who arrive. But I haven't tested the English version; if I do, it will be much later.