Why sinking a warship is not treated like bombing a city

How would other powers react if a major warship were sunk by an opposing carrier force at sea?

The loss would provoke doctrinal arguments, but it would be seen as part of naval war; diplomatic sanctions are more likely when civilian cities are attacked.

Rival navies would argue over maintenance, modernization, and the future of capital ships after a major loss. Fleet combat differs from attacks on cities because warships exchanging missiles or gunfire at sea already make the conflict unmistakably a war. Naval gunnery against opposing ships and shore headquarters illustrates the deliberate character of such violence. International reaction therefore turns on the scale of violence and whether the chosen targets are military forces or civilian communities.