So you might think that M.A.D only existed since the invention of nuclear weapons? Wrong!
Mutually Assured Destruction existed since always.
What is M.A.D? Is it the total and complete anihilation of every living creature in your country?
No, it's not. Is it the total anihilation of your whole population?
No, it's not.
M.A.D is the assured destruction of the existence of a viable state(it can mean the destruction of everything, but does not have to)
Say you have 2 ancient states one can field 100,000 soldiers the other 80,000 but they both can have a M.A.D policy toward each other.
If those 2 states go to war and anihilate each other armies which by the way are most of their men with reproductive capacity they are BOTH done!
Ever heard the term "Pyrrhic victory" - it's a soft form of M.A.D
Why do you think we still have 2 separate countries of France and Germany? although both countries fought many wars with each other and scored decisive victories in them? It's because a total anihilation of the other country was too costly and would have(in all likelyhood) trigger own demise.
Why do you never fight to the death in a bar fight? Because even if you kill your opponent you end up in jail for life so M.A.D again! But even if there was no jail and both parties would know that the fight is to the death the risk of getting seriously injured or killed would be too high to take it willingly.
Or why does a rattle snake alert you to it's presence? It's because it's advertising it's own version of M.A.D!
So keep that in mind. Everything in Nature is based on the M.A.D principle and if you don't have the M.A.D option than you are (by definition) prey.