désescalader

A modern borrowing from English "de-escalate," now standard in diplomatic and news French for reducing the intensity of a conflict (désescalader une crise, une tension militaire). It also keeps a literal, older climbing sense — to climb back down a rock face or wall.

• Les deux pays ont accepté de désescalader la crise. — The two countries agreed to de-escalate the crisis.
• Le grimpeur a dû désescalader la paroi à la tombée de la nuit. — The climber had to climb back down the rock face as night fell.
• L'ONU appelle les parties à désescalader immédiatement. — The UN is calling on the parties to de-escalate immediately.

Some style guides still flag désescalader as an anglicism and prefer apaiser or réduire les tensions in careful writing, even though it's now extremely common in journalism — worth knowing the word is accepted but not universally considered "pure" French.