England had for some years owned land in France. The barons had provided the king with both money and men to defend this territory. Traditionally, the king had always consulted the barons before raising taxes (as they had to collect it) and demanding more men for military service (as they had to provide the men). This was all part of the Feudal System.
So long as English kings were militarily successful abroad, relations with the barons were good. But John was not very successful in his military campaigns abroad. His constant demands for more money and men angered the barons. By 1204, John had lost his land in northern France. In response to this, John introduced high taxes without asking the barons. This was against feudal law and accepted custom.
