Your fortress has become that ark. This is the only place where people remained who were not overthrown by alien machines. They invaded your world on purpose and left no chance to engage in an equal fight. That is why you have become the commander-in-chief, who leads the remaining inhabitants of planet Earth forward.
You need to organize all people in such a way that everyone performs their functions. Someone will be busy strengthening the fortress, others will defend it. The third squad must engage in battle with the infernal legions of machines. Manage your wards.
You are their guiding light. It depends on your organization whether you can regain your lands. Open all available cards in the game. Create weapons that can withstand piles of metal. They are practically invulnerable. Everything is decided only by your skills and the preparation of soldiers to defend the fortress.