Although the English countryside was involved in numerous wars throughout all of its history, the time period between Beowulf's earliest attributed authorship in the 8th century to Geoffrey Chaucer's death in 1400 was a time of seemingly endless war and turmoil throughout all of Britain. The fall of the Roman Empire immediately left Roman-Britain open to invasions from the Germanic, Scandinavian, and Irish peoples of nearby countries, as well as the native peoples of Scotland and Wales.
This resulted in centuries of war, in order to gain control of the British island. The most successful foreign invaders of this early period would be the Germanic Angles and Saxons (Depicted in red and brown respectively).
However, starting around late 8th century, the British island (along with the rest of Europe) became a popular destination for invading Vikings. By the end of the 9th century Norwegian and Danish armies had established very large settlements in Britain.
Soon after the Battle of Hastings in 1066, invaders from Normandy, originally a Viking settlement in the Frankish kingdom itself led by William the Conqueror, laid came to just about all of what's considered modern-day England.
Throughout this time period, Beowulf, in its current form, was compiled from generations of folk tales of myth and war brought to Britain by the Germanic and Scandinavian invaders. The themes expressed in Beowulf such as, kinship, rivalries, honor, military prowess, religion, courage, good and evil, etc. are all universal themes that are understandable in all of these civilizations. Not only that, but along with the proud and die-hard religious attitudes of the poem, these are themes that are dealt with on a daily basis during this period in Britain.
Though, the matter of lordship and knighthood is treated as a sort of pro-military propaganda in Beowulf (as it was in most heroic epic poems), it was given a much less fantastical and more introspective treatment in The Wanderer. In this Old English poem, the knight is alone without a kingdom as his lord and his comrades were all killed in battle. Just as many kingdoms fell during this period, many knights found themselves wandering alone.
Norman England would soon become part of the Angevin Empire, which included the various kingdoms of modern-day France. However once that Empire lost its grip under the rule of King John, England would go on to have political unrest and be involved in various wars (both civil and foreign) most notably with the French and Scottish.
The political treachery, constant squabbling for the crown of England, and various social upheavals of the time would go on to further influence the (often more humorous) works of Chaucer, Shakespeare, and Donne as well. Knowledge of the history and culture of the time should is totally necessary for full appreciation of these authors and their works.