Well yes technically countries can just attack others. In practice they need to justify those attacks to their allies and populace if they want to maintain the status quo with them. That's where "they started it, we're only defending ourselves" is very helpful.
replyThe response is typically sending diplomats home, cancelling agreements, and sanctions. Something proportional. Not immediate outright war.
replyRomania has reluctantly done exactly that after the drone incident and tensions have escalated. The Romanians closed the Russian consulate in Constanta as a response and sent the consul back to Russia. The Russians sent an hijacked Ukrainian drone that blew up after 5 hours in the port of Constanta just after this. Now they're slowly escalating by periodically sending drones into Romanian airspace or attacking cargo ships bound from/to Odessa while in the Romanian EEZ.
reply> You don't need a real basis for a response. There's nobody here enforcing any rules.
replyFirst order, maybe. But the clearer the attribution the more political capital there is to act. Just look at the article. We don’t know, and won’t know for a while, if this was caused by Russia or the FDF protestors or who. That is all confusion all kind of actors can use to criticise a government who puts more sanctions on Russia.