As far as books are concerned, I would recommend to you The Hollow Crown by Miri Rubin as a good, readable intro to the period of English history you're interested in exploring. The book covers (I believe) the era from Edward III to the end of the Wars of the Roses and the ascent of Henry Tudor. Also, for a good textbook, I would recommend Early Modern England by Key and Bucholz. The book is thorough enough without getting bogged down in minutiae and is very well written.

From my own reading and research (and keep in mind, I only have an undergrad degree in European History, so someone else could have something much more valuable to contribute), England's monarchy was much more highly centralized that France's. France was fractured by internal divisions and was plagued by a comparatively weak monarchy that lacked the authority to call up the amount of manpower that would have been necessary to present a challenge to England. The French king held direct authority only over a very small region in France known as the Ile de France. However, even when the French king did have the ability to meet the English in battle with superior numbers, it still didn't go in their favor, most notably at Agincourt, which I'm sure you're familiar with.

I am very interested in this subject and am currently writing a senior thesis in college that covers a small part of this period. The best books by far are Jonathan Sumption's series on the Hundred Years War (volumes 1-4 of 5 are out), the cover both sides of the conflict in incredible depth and clarity in a way that a book focusing on the English or French said of things wouldn't

English success in the conflict, which was in fact a series of wars between the English and French monarchies that lasted from 1337-1360, 1369-1389, and 1415-1453, with periods of truce or peace in between, was due to multiple intertwined factors:

I. Political. First of all, as already said here, the English monarchy was much more "centralized." In a medieval this means that the king had legal authority over the entire country (except the Welsh Marches but that's a whole other subject) and their were no princes holding whole parts of the country with little more than a bond of homage to the king, as was the case in France. The English aristocracy was extremely powerful, but they were a national nobility with interests all over the country, and were more likely to challenge the king from the center than attempt to break away or all with another country. France, on the other hand, had always been a much larger country and a patchwork of different languages and political structures, in which the monarchy had only become the dominant political force around 1200. This process was very much incomplete, and several principalities on the edges of France had maintained an enormous amount of autonomy and functioned effectively as independent states in throughout the conflict. These were Flanders, Brittany and Aquitaine. Flanders and Brittany both had ties to England at the outbreak of hostilities, in the case of Flanders these ties were economic while the Breton dukes held the Earldom of Richmond in England. Aquitaine was ruled by the English dynasty, the last redoubt of what had once been a great empire covering all of western France. Both Flanders and Brittany allied with England at different parts of the war and neither principality was incorporated into France -- they would instead make peace with France at different juncture in the conflict.

II. Financial Due to the strength of the English monarchy, the English were much better able to raise funds at the beginning of the war. The weakness of the French monarchy prevented the creation of a permanent financial system until France was forced to in the 1360s in response the utter defeat by Edward III and his son the Prince of Wales. The next war, between 1369 and 1389, saw the English lose most of their gains from the past two generations. Henry V was once again able to raise huge amounts of money to finance his war between 1415 and 1422. In end however, France was richer and England could never keep up the expenditure to defend its continental conquests, leading to its ultimate expulsion from France in 1453, save Calais, which was lost in 1558.

III. Military. This is where the political and financial factors mixed with technological and strategic advances. The English pioneered a new fighting style. They raised large, well trained armies composed of men-at-arms and archers. Men-at-arms were basically Late Medieval knights, elite soldiers in plate armor with good horses -- but who were not always of noble birth -- knights fought with men-at-arms and in the same way but military needs required a larger pool of soldiers of this type. English archers used longbows, which proved more effective than crossbows, that could cause incredible devastation to enemy cavalry. These English armies fought together for extended periods and function as units far better from their French counterparts. English armies were entirely mounted, yet fought on foot. The famous battles of Crécy, Poitiers and Agincourt were all fought with a novel formation in which the men-at-arms were massed in the center while the archers were placed on the sides, slightly in front of the men-at-arms. This was used in other battles as well. The French had less unified armies that would be formed for a specific campaign, and remained much more attached to cavalry warfare. One could say French knights were more attached to their chivalry than English ones, who learned the efficacy of fighting on foot.

IV. Personality. The personality of leaders is always crucial to events, and few periods speak more to this than the Hundred Years War. The English had several incredible war leaders, like Edward III, the Black Prince (Edward III's son who died a year before his father) and Henry V, as well as a number of excellent captains, for example Henry of Grosmont, Duke of Lancaster or later on the Earl of Salisbury. They were able to out-think, out-strategize and out-fight their French enemies time and time again. It is no coincidence that the periods of French success were when they had the strong kings such as Charles V and Charles VII, while they were defeated during the reigns of the incompetent kings Phillip VI, John II and the insane Charles VI. Furthermore, Henry VI was a nonentity who went insane later in life as well (probably due to being Charles VI's grandson!) was king during England's final defeat in the beginning of the 1450s.

I hope this answers your question. For more, go to Sumption's books, where I got much of this information. Other good books on the period would include:

• Michael Hicks' "The Wars of the Roses" for the civil wars following England's defeat.
• Barbara Tuchman's "A Distant Mirror" for an excellent pop-history telling of the 14th century.
• Malcolm Vale's "English Rule in Gascony 1399-1453" for an excellent monograph on the English administration in Gascony during the later part of the Hundred Years War.
• Richard Vaughan's multi-volume history of the Dukes of Burgundy.

I think part of your confusion may stem from the fact that it was not just a war between modern day England and France. There was a very large portion of land in France that belonged to the king of France. Here is a map that shows some of the land that was under control of England. The King of England had lands in Normandy and Acquitane. The other thing is that France was not a single state as we think of today. A monarch did not really have the ability to muster all of the resources of the state and prepare for total war. Even state is not really an entirely correct word to describe the situation. The hundred years wars is part of the transition from a French feudal society to a more modern nation state. There were nobles that had mixed loyalties, and that what the war was fought over. How much authority did the King of France have.