Beloyar
Demigod
There should be plenty of ways to attack without revealing nationality. In the real world, you can sink a transport or passenger ship by submarine without anyone finding out who is responsible.
Also, you can launch a missile from a submerged sub and no one will know whose sub it was.
This, of course, requires progressive civs to keep tabs on others who have the technology to develop and build such weapons.
It would be imperative to have national leaders who you trust not to attack you, while at the same time have some means to track the origin of attack and eventually (not immediately) find out who was responsible.
Also, you can launch a missile from a submerged sub and no one will know whose sub it was.
This, of course, requires progressive civs to keep tabs on others who have the technology to develop and build such weapons.
It would be imperative to have national leaders who you trust not to attack you, while at the same time have some means to track the origin of attack and eventually (not immediately) find out who was responsible.