As explained by The Economist.
"In 1215 England’s King John was in trouble. He had spent heavily on a
failed attempt to regain bits of France; the French were threatening to
invade; rebellious barons, whom he had been fleecing to finance his
wars, were marching against him. He had no choice but to sue for peace
with the rebels; the peace treaty, sealed at Runnymede on the Thames on
June 15th, was called the Magna Carta."
"Since the barons had the upper
hand, its main thrust was to protect their rights against monarchical
"It did not, as some suppose, spawn democracy (which only started
to emerge even in embryonic form rather later) or trial by jury (which
was already in use). But its chapter 39 (29 in subsequent versions)
asserted the right to due process of law—“no free man shall be seized or
imprisoned...except by the lawful judgment of his equals or by the law
of the land”—for which it has been revered ever since."