King John of England muscled by barons. Some power shifts from the king to the nobles.
The Magna Carta required King John of England to proclaim certain rights (pertaining to freemen), respect certain legal procedures, and accept that his will could be bound by the law.
Most Western history books treat the Magna Carta as an epochal document.
It is far from clear that in the short run (before the English Civil War of 1641–1651), the rights of anyone except those of the nobles increased.
a.k.a. Magna Carta Libertatum (the Great Charter of Freedom).
It was amended several times, and it is the 1297 CE version which remains on the statute books of England
and Wales.