What medieval practice tried to stop private wars among nobles?

The story behind the answer

A Church-led initiative of the late 10th–11th centuries tried to rein in endemic noble feuding by banning combat on specified days (often from midweek evening to Monday morning) and during Advent, Lent, and major feast days, with violators threatened with excommunication. By shrinking the calendar of permissible violence, it made private war riskier and less disruptive to agrarian life and worship.

It worked alongside the related Peace of God, which protected noncombatants and sacred property; the “truce” targeted the timing of warfare instead. Originating in southern France and spread by church councils and sworn oaths, it never fully eliminated feuds but helped channel knightly violence, influenced chivalric norms, and foreshadowed later royal claims to monopolize legitimate force.