What can prevent wars like civil war from happening?

one side would have to agree and be on the same terms with the opposing side

Explanation:

To end the civil war, one side—usually the rebels—must agree to disarm and demobilize. But in the absence of a third party who can guarantee their health, rebel groups fear that the government will only wait for them to surrender and then destroy them. Rebel groups could then withdraw from the negotiations.

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