This is unrealistic for smaller countries, like Ancient Greek poleis or contemporary Estonia. Under your logic, they would have to give up their existence and join some empire.
In practice, already the Greco-Persian wars are an indication that alliances of smaller nations are viable, and that they are more efficient due to specialization. This is not a new problem, nor is it specific for post-industrial history; the Athens were better at fighting at sea, other poleis could provide hoplites.
This is unrealistic for smaller countries, like Ancient Greek poleis or contemporary Estonia. Under your logic, they would have to give up their existence and join some empire.
In practice, already the Greco-Persian wars are an indication that alliances of smaller nations are viable, and that they are more efficient due to specialization. This is not a new problem, nor is it specific for post-industrial history; the Athens were better at fighting at sea, other poleis could provide hoplites.