Why did English barons oppose King John’s campaign in Poitou?

English barons, particularly those in the north, strongly opposed King John’s military campaigns in Poitou for several reasons related to the king's governance and financial demands.1

• Financial Burden: John’s efforts to reclaim his French territories were extremely costly. To fund these wars, he imposed heavy financial burdens on his subjects, including unpopular taxes like the "13th" in 1207 and the levying of massive reliefs—inheritance duties that could reach thousands of marks.1
• Abuse of Power: The barons viewed John’s rule as increasingly oppressive. His administration was marked by a disregard for established law and custom, and he frequently exploited his feudal prerogatives to extract wealth.12
• Personal Rule: Unlike his predecessors, John spent most of his time in England, which made his direct and often arbitrary exercise of royal authority feel more intrusive to the baronial class.1

Ultimately, the resistance to the Poitevin campaign became a focal point for broader grievances, leading many barons to protest against John’s disregard for feudal rights and the law, culminating in the events that led to the Magna Carta.1