The Percys had supported Henry IV in a war against Richard II, which ended when Henry took the throne in 1399. Henry had been supported by a number of wealthy landowners to whom he had promised land and money in return for their support. When the war ended lands in Cumbria promised to the Percys were instead given to a rival. This was enough to spark them into revolt, which may have been helped by money promised by Henry which never arrived.
Henry Percy raised a small group of retainers, likely about 200, in early July 1403 and started marching south to meet his uncle, Thomas Percy. He recruited most of his army in Cheshire, an area hostile to Henry IV,and which provided many experienced soldiers, notably its archers, some of whom had served as Richard II's bodyguard. It appears that he may have hoped to be reinforced by a Welsh force under the self-proclaimed Prince of Wales, Owain Glyndwr. This didn't happen, although it appears some Welsh from the borders may have joined him. The rebels then marched towards Shrewsbury, the easily defended county town of Shropshire.
King Henry became aware of the situation on July 12, apparently while he was moving to help the Percys from another threat. Upon hearing of the forces, he changed direction and marched towards Shrewsbury with his army. Estimates of the sizes of the two armies vary widely, with the Royal army being placed between 15,000 and 60,000, and the rebels between 5,000 and 20,000.
Both forces arrived near the town on July 20 1403 and set up camp to the north and south of the Severn River, which loops around the town. The next day the King's forces crossed the river at Uffington, placing them in a position in open ground where they could best use their large numbers. They were soon joined by the Percy forces from the north.
For much of the morning the two forces parleyed. It appears that Henry was somewhat inclined towards accepting the King's position, while his uncle Thomas was not. Whatever the case, negotiations ended near noon, and the two forces advanced for the fight.
The battle opened with a massive archery barrage, killing or wounding many of the men before they could meet in the field. Of the two forces, the Percy's Cheshire bowmen proved generally superior. However when the two armies finally met, the greater numbers of the Royal army generally prevailed. The Percys attempted to address this imbalance with a charge, but it was premature and Heny Percy was killed. At this point the rebel forces fled the field, and a rout began. Over 300 knights and another 20,000 men-at-arms fell on the field, and thousands more died of injuries over the next few weeks.
Henry Percy was initially buried at Whitchurch, Shropshire, but rumors soon spread that he was not really dead. In response the King had him disinterred. His body was set up in Shrewsbury impaled on a spear between two millstones, and was later quartered and put on show in the four corners of the country. In November his remains were returned to his widow.