The English parliament passes more anti Welsh Laws. But to no avail. The Welsh people show more support for Owain and the rebels are fortified by the defection of hundreds of experienced Welsh archers from service in England.
The English pay the 10,000 marks ransom to free Reginald De Grey. This helps to fill Glyndwr's war chest

By the end of 1402 the rebellion was really heating up, and the action became truly national. In 1403 Glyndwr headed to the South and the West. His forces marched down the Tywi Valley gaining support as they went. English Castles and manor houses fell in their wake. Indeed Carmarthen Castle fell to the Welsh.
He then headed West attacking Glamorgan and Gwent. Abergavenny and Usk Castles were attacked and burnt. before taking Cardiff and Newport.

Keys of Carmarthen Castle are handed over to Owain Glyndwr. With his army now 8000 strong this could be said to represent the almost total collapse of English rule in Wales at that time
Henry Percy (Hotspur) son of the powerful Earl of Northumberland, but also brother in law to Mortimer defects from the English cause to support Mortimer and Glyndwr.
Henry Percy gathers support from the Welsh and Cheshire-Welsh Border folk and heads for Shrewsbury.
Glyndwr heads North to Shrewsbury
Northumberland heads South to Shrewsbury to support his son Hotspur.
King Henry IV who had been heading North to Scotland turns his English army and marches to meet his son Prince Henry at Shrewsbury.
They arrive first at Shrewsbury and force Henry Hotspur to fight before his reinforcements have arrived. On 21 July their combined forces defeat the army of Henry Hotspur who is killed. Over 300 knights and up to 20,000 men are killed or injured.

Surprisingly this was not a serious setback for Glyndwr, he and Northumberland had not arrived in time to join the Battle of Shrewsbury

Harlech Castle falls to the Welsh. Aberystwyth Castle soon follows suit. French are continuing to attack Caernarfon Castle.
Owain garrisons the captured Castles, establishes court and sets about demonstrating his vision of a Welsh Nation. He calls a Parliament in Machynlleth and in the presence of envoys from France, Scotland and Castile is crowned Owain IV Prince of Wales

Owain sends envoys to seek aid from Charles VI of France. Charles is sympathetic being the father in law to the deposed King Richard II

Treaty agreed between Glyndwr and the French.
Welsh continue to harass the English Border

60 French ships with 700 men sail from Brittany and Normandy. But they return to France in November without actually landing in Wales

By the end of the year the French ships were raiding the coast of England, with Welsh troops on board, setting fire to Dartmouth and devastating the coasts of Devon. The Tripartite Indenture, the agreement between Glyndwr Northumberland and the Mortimers however did not come to fruition. The Percys of Northumberland failed in their efforts in the North. The plan to free the Mortimer heir and to kick start  an uprising in England against King Henry failed to materialise, and Glyndwr suffered setbacks in Wales

The Tripartite Indenture was signed in Bangor North Wales. The agreement was between Owain Glyndwr, the Earl of Northumberland and Edmund Mortimer.
They undertook to divide Britain into three parts.

• Glyndwr would take Wales and the West of England as far as the rivers Severn and Mersey including most of Cheshire, Herefordshire, and Shropshire.
• The Mortimers would take all of Southern and Western England
• Thomas Percy, the Earl of Northumberland, would take the North of England and as far South as Leicester, Northampton, Warwick and Norfolk

Welsh defeat in the Monnow Valley

Owain's eldest son Gruffudd was defeated and captured at Pwllmelyn  near Usk. He was taken to the Tower of London where he died of the plague 6 years later.
Owain's brother Tudur was killed at Usk.
According to Adam of Usk, Prince Henry had three hundred prisoners beheaded in front of Usk Castle after the battle

English sail from Dublin and attack Anglesey. The Welsh eventually abandon Anglesey and retreat to the hills of Snowdonia

Two thousand six hundred French land at Milford Haven. Joining forces with Glyndwr's own ten thousand men they marched inland and took the town of Haverfordwest. They then moved on and retook Carmarthen and laid siege to Tenby. Owain took control of the Teifi Valley and then with the West secure they marched East. By the 22nd August Owain and the French confronted Henry at Woodbury Hill, Worcester. The confrontation lasted for eight days. What happened next is a mystery to this day. No battle took place, other than skirmishes. Glyndwr retreated into Wales.

Henry invades Wales again. Again the Welsh weather attacks Henry and the English army. He loses his baggage train  in flash floods and 40 wagons fall into the hands of the Welsh. Henry retreats to Hereford.

Some of the French army return to France

In 1406 the French withdraw. The French and the Welsh had different priorities. The Welsh wanted to secure an independent Wales, but the French were more interested in invading England. The Welsh were involved in fighting between castles in Wales. The French wanted a full scale invasion of England but it was not Glyndwr's priority to take the crown of England

In a further effort to secure French help Glyndwr wrote to the King of France from Pennal near Machynlleth offering to transfer the allegiance of Wales from the Pope in Rome, as recognised by England, to the Pope in Avignon, as recognised by France. It was to no avail, the French did not respond

French finally withdraw their help. The Welsh start to lose battles. The Scots are unable to offer help as the young Scottish King is held hostage in England.

Resistance in Anglesey (at one time the heartland of the rebellion) formally ends

Harlech and Aberystwyth Castles are beseiged by the English

Earl of Northumberland dies in Yorkshire

After a long seige  Aberystwyth Castle falls to the English on 23rd September

Harlech Castle falls to the English. It must have been dreadful in the besieged Castles. Many died including Edmund Mortimer. Glyndwr and his only surviving son Maredudd escaped, but his family was captured, including his wife Margaret, his two daughters, and the three Mortimer grandchildren. They were all to die in the Tower of London before 1415