It was fortunate for Henry V that someone on the Orleanist side of politics decided to murder the Duke of Burgundy. This persuaded the new duke, Philippe the "Good" to take Henry's side, a development which led to the Treaty of Troyes and Henry's marriage to fair Catherine of France. Henry had by this time conquered a fair chunk of Normandy, but this had stretched his resources considerably. Thanks to the new alliance he could paint himself as the legitimate ruler of France, and some Frenchmen, like Burgundy, were willing to come over to his side.
At the same time, although the cause of the Dauphin and the Orleanists looked bleak, the fact remains that they were in possession of the majority of French territory and the resources that went with it. Henry would need to conquer this, castle by castle, town by town, and every new garrison needed more soldiers and the means to supply them with necessaries.
The bright spot was that the conquered territories did provide a source of revenue. The bad news was that the English Parliament was increasingly of the view that the war was "nothing to do with us, guv." In short, they saw the conquest as Henry's conquest rather than England's, and, in their view, it was up to Henry to defeat his "rebels" at the expense of the Kingdom of France.
That a typical Englishman of this time had his chest swelled with pride at the thought of English military glory, but at the same moment did not want to pay towards the costs should not really surprise us. It was a characteristic of the English almost all the way through.
Henry V's early death in 1422, with nothing really resolved, was another good example of the "hospital pass". To Henry V, the glory, to Henry VI the criticism for failing to do the impossible.
It was fortunate for the English that the management of their position in France fell to John, Duke of Bedford, Henry V's next surviving brother, who just happened to be one of the most able men to grace the entire middle ages, let alone the fifteenth century. Bedford won a stunning victory at Verneuil (1424) which was, if anything, more impressive than Agincourt, though rather less famous.
After that, though, the Anglo-Burgundian position slowly but surely began to deteriorate. There were a number of reasons for this, and one was certainly that Philippe of Burgundy was never 100% committed, except to his own interests. Another key factor was that French gradually improved their military establishment, not least by investing heavily in artillery. But above all, the limitations of English resources in terms of both men and cash became increasingly apparent as the years went by.
As I have remarked before, what is astonishing about Lancastrian France was not that it fell when it did, but that it lasted so long. The Treaty of Arras (1435) detached Burgundy from the English side, and that should have been the end. As it was, the English were not finally expelled from Normandy until 1450, while the last English intervention in Gascony failed in 1453. The tactics of Agincourt no longer worked. The French had developed a well-organised, well-equipped, professional army, while England struggled to raise field armies of any size at all.
Much of this prolongation of the war was down to English pluck and determination, to say nothing of good fortification, but it was really a hopeless cause. If Henry VI had been a more talented ruler - which would not have been hard - or if some of his generals (notably the first Duke of Somerset) had been a bit more inspired than they were, then maybe, just maybe, the disaster might have been stretched out a little longer. Alternatively, if certain English statesmen - notably Humphrey of Gloucester - had been more realistic and less deluded, then something might have been saved of the English possessions in France. As it was, a losing fight against overwhelming odds could only have one end.
The effect on England, as a nation, was disastrous. The self-image of a country that was a great military power was shattered. The treasury was not only empty, but massively in debt, despite years of war taxation. The King's government was feeble at best, and disorder was commonplace, even to the extent of outbreaks of fighting between rival families. Of course, it must be admitted that Henry VI was one of our least effective monarchs, and that his tendency to favour the incompetent Beauforts over the (relatively) competent Duke of York did not help. The political crisis began long before the final defeat in France, but that defeat added a whole new level to it.
Since all attempts at political compromise failed, it was all but inevitable that what we now call the Wars of Roses should break out, even though the first "battle" (St. Albans 1455) was little more than an unseemly squabble. But the root of political instability in England was the disastrous policy of war with France.