And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus.
–        Philippians 4:7

The Birth of the West: Rome, Germany, France, and the Creation of Europe in the Tenth Century, by Paul Collins

Charlemagne's attempt at consolidation and empire ended in failure and chaos, especially in his original domain – the land of the Franks, the western lands of continental Europe.  Within a couple of generations, war, battles, highwaymen, theft: a drive for kingship and emperorship by some, a fight for survival by many.

The church tried to stem the extent of feudal warfare through "the peace of God."

This wasn't faith without works or words without action.  The movement began with the bishops and was spread by the bishops.  It might be considered one of the first popular movements in the medieval west, beginning in 989 at the monastery at Charroux, and then spreading in subsequent years to Le Puy (990), Narbonne (990), Limoges (994), and Poiters (1000).  Orleans and Burgundy subsequently followed.  The assemblies were held in open fields, with ever-larger crowds participating.

Excommunication was the threat used to reign in the recalcitrant:

Those who refused to keep the peace were excluded from Mass and Communion, refused forgiveness of sin, and denied church burial in consecrated ground, which effectively condemned them to hell.

Citing Ronald C. Musto:

In an age when salvation was the goal of life, such measures were of incalculable power.