Henry may have regarded the assertion of his own claims as part of his Kingly duty, but in any case a permanent settlement of the national debate was essential to the success of his world policy.
;1415 campaign
Henry sailed for France on
11 August, 1415 where his forces besieged the fortress at
Harfleur, capturing it on
22 September. Afterwards, Henry was obliged to march with his army across the French countryside with the intention to reach
Calais. On the plains near the village of
Agincourt, he turned to give battle to a pursuing French army. Despite his men-at-arms being exhausted and outnumbered, Henry led his men into battle, decisively defeating the French. With its brilliant conclusion at
Agincourt on the
25 October 1415, this was only the first step.
;Diplomacy and command of the sea
The command of the sea was secured by driving the
Genoese allies of the French out of the
Channel.(His flagship, Grace Dieu – 1420)
A successful diplomacy detached the emperor
Sigismund from France, and by the
Treaty of Canterbury paved the way to end the
schism in the Church.
;1417 campaign
So, with these two allies gone, and after two years of patient preparation since
Agincourt, in 1417 the war was renewed on a larger scale. Lower
Normandy was quickly conquered,
Rouen cut off from
Paris and besieged. The French were paralysed by the disputes of
Burgundians and
Armagnacs. Henry skilfully played them off one against the other, without relaxing his warlike energy. In January
1419 Rouen fell. By August the English were outside the walls of
Paris. The intrigues of the French parties culminated in the assassination of
John the Fearless by the
Dauphin's partisans at
Montereau (
10 September, 1419). Philip, the new duke, and the French court threw themselves into Henry's arms. After six months' negotiation Henry was by the
Treaty of Troyes recognised as heir and regent of France (see
English Kings of France), and on
2 June 1420 married
Catherine of Valois the king's daughter. From
June to
July his army besieged and took the castle at Montereau, and from that same month to
November, he besieged and captured
Melun, returning to England shortly thereafter.
;1421 campaign
On
10 June, 1421, Henry sailed back to France for what would be his last military campaign. From
July to
August, Henry's forces besieged and captured Dreux, thus relieving allied forces at Chartres. That
October, his forces lay siege to
Meaux, capturing it on
2 May, 1422. Henry V died suddenly on
31 August 1422 at
Bois de Vincennes near
Paris, apparently from
dysentery which he contracted during the siege of Meaux. He was 34 years old. Before his death, Henry V named his brother
John, Duke of Bedford regent of France in the name of his son Henry VI, then only a few months old. Henry V did not live to be crowned King of France himself, as he might confidently have expected after the Treaty of Troyes, as ironically the sickly Charles VI, to whom he had been named heir, survived him by two months. Catherine took Henry's body to London and he was buried in Westminster Abbey on
7 November 1422.
Following his death, Catherine would secretly marry or have an affair with a Welsh courtier,
Owen Tudor, and they would be the grandparents of King
Henry VII of England.