Consequences of the Hundred Years' War

Which country suffered more through and at the end of the Hundred Years' War; England or France?
What were the economic impacts? Political impacts? Social impacts?
I've heard that it nationalised France, but does that imply England was already nationalised? Is that why England (the smaller country) did remarkably well for a long while?

I can answer your last question somewhat.
One important factor that meant the war was fought in France was the English victory at Sluys. Philip's entire navy was destroyed giving the English navy mastery of the channel. This allowed invasion of France to occur unimpeded, but the reverse to be impossible

The HYW nationalized both countries. It is actually pretty interesting to study how the conflict began as a feudal war between the Plantagenêts and the Capets and ended as a national war between France and England. Most of this patriotic sentiment was born out of great xenophobia in England, and as a way of uniting the country against the miseries the english caused in France.
The war ended as a great victory for France, as Charles VII ended the war by crushing all of the opposing factions, save for Burgundy which his son will have to deal with. The war developped the french administration and royal power, with the King now having a permanent military and a personnal artillery. In England it increased the power of the Parliament and it is this that doomed the King of England in the end : After 1453 the parliament refused to raise new taxes so he could start a new expedition in France, as the Chamber of Commons found no use in a war in which the union of France and England would simply be beneficial to France and frenchmen.

That's pretty wrong actually, because the HYW lasted for a 100 years and the situation quickly reversed itself because of the talented french general Jean de Vienne ; He took part on the Crusade of the Count of Savoy, Amédée, which is where he grew fond of ships and navies. He convinced the King Charles V to build a large navy and a new arsenal in the Clos des Galées, near Rouen. While nothern Europe wasn't known for their knowledge of naval battles or strategy (It was mostly trade ships hitting each other in the front without any more sense of tactical planning), Jean de Vienne used ships as an act of revenge against the english Chevauchées. After the castillian victory of La Rochelle in 1372 where the english ships burned down, Jean de Vienne conducted numerous raids on the English southern coast, which brought terror and encouraged a new peace, especially as Bertrand du Guesclin liberated the territories captured by Edward III.
However, after King Charles V's death, the new king Charles VI, who was much more traditionnalist, closed down the Clos des Galées. Jean de Vienne was angry about that and searched for a new adventure elsewhere ; He died against the turks at Nicopolis.

France because it went centralised which is crypto feudalism whilst England saw the rise of parliament which was good for all decent men

Could England have continued to fight had parliament not refused to support the war?
I never really understood how the war was feasible for England. They had 1/5 of France's population and they were the offender yet the war lasted 116 years. What was the difference between the two nations that permitted this?

Because they held Aquitaine, France was very decentralised, burgundy helped at one part, captured the king, had better tactics so on and so on

How and when did England become centralised?
Why did Burgundy help?

First of all, the fact that the Kings of England rested a lot on factionnalism and civil troubles in France to conduct their campaigns ; Charles the Bad of Navarre was for exemple a friend of Prince Charles, the son of Jean II the Good, which you may guess is problematic when Charles the Bad has a secret alliance with Edward III of England to invade the country. In 1415, when Henry V lands in France, the country is torn apart by a violent civil war between the Armagnac and Bourguignons, where peasants have to arm themselves if they don't want to get hanged by ravaging bands of thugs.
England always relied on local allies in France to conduct their campaigns. The gascons and the normans (At least until John Talbot fucked up and started to hang rebellious normans) supported their armies and gave them soldiers.
Population is important for the power of a country, but the HYW was not a total war like it would happen in later centuries ; The armies of England and France never exceeded a few thousands. In fact the english used their lower number as an advantage, by relying on the chevauchée instead of multiple sieges, and by having small, maneuvrable and coherent units while the King of France, for most of the war, had to contend with an aristocracy, mercenaries and communal levies where you could find the best and the worst ; Before the battle of Agincourt, the experienced Boucicaut asked the officers not to charge the englishmen, but he had to share command with young noblemen who knew nothing of war except for tourneys.
After 1453, there was another attempt at invading France ; But Louis XI, who was a political genius more than a astute commander, paid off Edward IV of England at Picquigny to break his alliance with the Duke of Burgundy ; Afterwards, Louis XI had his hands free to make sure the swiss could fuck up Charles the Bold and get his lands.

England had increasingly become centralised upon Alfred the Great’s accession
Burgundy and argmangnac were suppoused to act as equals when being regents to the mad French king, but then the argmanacs murdered the duke of burgundy so his son allied with the English king
Burgundy later re-aligning himself with the king of France is ultimately why the Plantagenets lost the 100 YW