During much of the High and Later Middle Ages, "England" was part of a much wider European cultural and political context. Although difficult to summarize within a few paragraphs, in any discussion of England in contrast to Europe, it's first important to understand the deep political links that England had with other European kingdoms during the medieval period.

During the first half of the 11th century, England was ruled by King Cnut the Great, who also happened to be king of Denmark and Norway. At this point he ruled over all of what is now England, with the exception of Cornwall and parts of Cumbria, north into southern Scotland. During this period of the "North Sea Empire," Danish rule, although it was too short to leave as much lasting social and political impact as the later Anglo-French rule, did integrate English politics into wider European political contexts. After Cnut died, control of England shifted between various members of the Anglo-Saxon and half-Danish royal families, until William the Conqueror invaded England in 1066 from Normandy.

William was Duke of Normandy, and his granddaughter, the Empress Matilda (who is a fascinating historical figure in her own right) married Geoffrey Plantagenet, who was the count of Anjou, Touraine, and Maine in what is now France. Their son, Henry II inherited all of these titles and added the duchy of Aquitaine in southern France to the lands under his control once he married Eleanor of Aquitaine. This ushered in a period of rule where England was only a part of a greater empire which, at its peak, stretched from the Scottish borderlands all the way down to the Pyrenees in southern France, and included nearly half of what is now France. All of this was ruled by the Plantagenet/Angevin dynasty. Most of the Plantagenet kings could be considered to be more culturally French than English. They communicated mainly in French (English did not become a common language amongst the Anglo-French nobility until later in the Middle Ages). Cultural interchange, interestingly, did go both ways - this was the period of time when Arthurian legend became wildly popular in France (see the works of Chretien de Troyes as a prime example).

The Plantagenets held England in their own right, but their French duchies and counties were held under the feudal lordship of the kings of France, which led to some fairly complex political problems (leading directly to the Hundred Years War). England did have the significant advantage of having a relatively well-developed legal and administrative structure, inherited from the Anglo-Saxon kings and significantly improved by Henry II, enhancing its importance within the wider domains. The English kings did not lose the last parts of their French holdings until the end of the Hundred Years War in 1453 - the very end of the Middle Ages as normally understood, although the holdings in France, for the most part, had been dwindling since the reign of King John. England was a separate kingdom and was not the same as the counties and duchies in France held by the Plantagenet kings, but at the same time it was ruled by the same individuals and the same families, and so to a certain extent, the "power and wealth" held by England during this period of time is difficult to fully separate from what was going on in continental Europe.

Of course, after the reign of King John, it does become easier to make this distinction as the English kingdom itself became comparatively richer and more central to the English monarchs as they needed to spend progressively less time and energy administering their continental domains. However the Hundred Years War itself (which was caused, in part by a complex question of dynastic and feudal succession) displayed how closely entwined the English and French power structures were during this whole era.

Further Reading: The Government of Philip Augustus: Foundations of French Royal Power - John W Baldwin, 1991 Tales from the Long Twelfth Century: The Rise and Fall of the Angevin Empire - Richard Huscroft