should preemptive strikes be allowed?

What justifies war?
1. war should only be fought in self-defense.
2. it should be declared only by the legitimate authority in charge of a nation-state.
3. it should be fought only after a negotiated solution has failed, as a last resort.
4. it should be fought with proportional means which avoid civilian collateral damage.
5. atrocities should not be allowed.
6. pows should be protected under the Genera convention.
7. environment poisoning should be forbidden.

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