Throughout the later 1300s and 1400s the family called Percy emerged as the most powerful barons in Northumberland and played a big part in the border warfare that constantly troubled the region. Only the Nevilles, an equally powerful family of Durham and Yorkshire could match the Percys in status.

In Durham, the Nevilles held the great castles of Raby and Brancepeth. The Percys, who were Earls of Northumberland from 1377 held the great border strongholds of Alnwick, Warkworth, Bamburgh and Prudhoe Castles.

The most famous Percy of them all was 'Harry Hotspur' a son of the Earl of Northumberland and a character immortalised by Shakespeare. Hotspur regularly fought in battles against the Scots and was particularly keen to fight his archenemy, the Scottish Earl of Douglas.

On one raid in 1388 the Scots under Earl William Douglas raided Durham as far south as Brancepeth and on their return engaged in a skirmish at Newcastle where English forces under 'Hotspur' remained safe behind Newcastle's walls. However as the Scots headed home they encamped at Otterburn in Redesdale in Northumberland. Here Hotspur and his troops, who had marched north from Newcastle, ambushed the Scots as they slept.

Unfortunately for the English, in the darkness Hotspur mistakenly attacked the Scottish servants and camp followers. This alerted the main Scottish force and in the resulting chaos Hostpur lost over a thousand troops in the battle. Douglas lost only two-hundred. Hotspur's men quickly fled but Douglas was killed despite the Scottish victory. Hotspur and his brother Ralph Percy were taken prisoner by the Scots and were later released for ransom.

The Scots were invading the north again in 1402 this time under the leadership of Earl Archibold Douglas who attacked Newcastle, before retreating. His forces were stopped by the English under Earl Percy at Humbleton Hill near Wooler in Northumberland and were defeated in battle.

Later, the Percys fell into disagreement with the English king Henry IV over Scottish prisoners taken in the battle and the Percys increasingly rebelled against King Henry.

Ultimately this would result in Hotspur's death in 1403 after he was killed in battle at Shrewsbury fighting against the English king. King Henry sent Hotspur's head to Hospur’s widow in Northumberland.

In 1406, the Scottish King Robert III (who had reigned since 1377) passed away and his son James I aged only eleven, succeeded to the throne. The Scots feared for James' safety and shipped him off to France for protection. It seemed a good idea but proved to be a disaster for the Scots. Pirates near Flamborough Head just off the Yorkshire coast captured the young king as he made his journey south. He would be imprisoned in various parts of England for the next eighteen years.

Finally in 1424 a meeting was held at Durham City between the English and the Scots in March of that year in which it was agreed that James could be exchanged with the Scots for English hostages. The peace treaty, called the Treaty of Durham was signed in the hope of bringing peace to the Borders. James spent a month in the hospitality of the Bishop of Durham while negotiations took place and he was eventually escorted to the abbey of Melrose for the exchange.

It did not of course bring peace and raiding continued. In 1428 the Scots plundered Alnwick and although the truce was renewed (this time at York) peace was still centuries away. Throughout the later centuries, the raiding continued and there were still occasional skirmishes between the Percy and Douglas families. However as the century drew to a close a new style of border warfare involving many lesser families was slowly beginning to emerge. This would be the age of the Border Reivers.