Under international law, when can a country declare war on another?

Was it legal for Israel and the United States to have carried out "pre-emptive" airstrikes across most of Iran’s provinces, which started the war? The USA says the attacks were justfied, because of an imminent threat from Iran's nuclear programme, and Israel claims it acted in self-defence.

The Israeli President went further - telling the BBC that focusing on the legality of the war instead of regional security is "mind-boggling" to him.

And what of Iran's response? Was it reasonable under international law? In the last few weeks, practically all its Gulf-state neighbours have been targeted, as well as its drones or missiles landing in Syria, Cyprus, Turkey and Azerbajan.

So does the Iranian retalliation justify the American and Israeli attacks under international law?

And if any country breaks international laws - are there any real consequences?

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