Why did king john lose most of his empire?

King John lost most of his empire due to a combination of poor leadership, military defeats, and conflicts with powerful nobles. His inability to effectively manage his territories, particularly in France, led to significant losses, including the loss of Normandy in 1204. Additionally, his oppressive taxation and disputes with the barons fueled discontent, culminating in the barons' rebellion and the signing of the Magna Carta in 1215, which diminished his authority and control.