At what point is ok or even necessary to declare war and enforce physical violence on a nation or group in self defense of the economic whole?
Declaring war and defense isn't only when there's a threat economically. But mostly, when there's a threat to the nation's security and that's what most country does.
Just as we can see with the Ukraine-Russia war.
It's about the security threat that Ukraine sees by the attacks made by Russia. And on the side of Russia, they saw those troups that are going near their border and they've find it as a threat as well.