[sssilver]

Preventive war (attacking to neutralize a future, non-imminent threat) is considered illegal under modern international law. The UN Charter restricts the use of force to UN Security Council authorization or self-defense against an actual, imminent armed attack, making preventive actions, which target potential future dangers, unlawful.

[jasomill]

It also allows any one of the five permanent members of the UN Security Council, including the US, to unilateraly veto any binding resolution that imposes sanctions for violating said law, with no established rules or even informal expectations that they recuse themselves when conflicts of interest arise.

[flyinglizard]

Israel and Iran are involved in active hostilities for a long time now, direct or by proxies. Furthermore, US and Israel are making the case for a preemptive war with the advent of the Iranian nuclear program (whether you believe it or not, that’s beside the point), and those are legal.