Wales, a region of rugged mountains, moors and forests, is noted for its large coal deposits. Its people are known for their strong Celtic heritage and renowned choral groups. This region was originally populated by an Iberian people, who were overrun by the Celts in the 6th century BC. The wealth of the British Isles attracted the attention of the Roman Empire, who first sent expeditions led by Julius Caesar in 55 BC and then invaded the island nation under Claudius in 43 AD. Julius Agricola, who became Governor of the new province of Britannia in 78 AD, completed the conquest of Wales by building a network of roads and erecting a substantial number of forts. A Roman legion composed of over 10,000 soldiers was garrisoned at Caerleon in the south of what is now Wales. However, the Romans abandoned the region after nearly four centuries of rule during the early 5th century. The imperial legions were recalled to Rome in an unsuccessful attempt to defend the empire from the barbarian tribes. The Romans that remained were expelled by the Britons in 409 AD.

The Britons soon faced conquest by a new wave of invaders. During the 5th and 6th centuries, Germanic tribes led by the Angles and the Saxons began to settle in England. The newcomers subjugated the Celtic inhabitants. The Britons who were not assimilated, enslaved or massacred were slowly driven out of their homelands. By the mid-7th century, the Anglo-Saxons had entrenched themselves in eleven kingdoms, including Northumbria, Mercia, Wessex, Kent, Essex, Sussex and East Anglia, which were collectively known as the Heptarchy. Meanwhile, the Britons had retreated into the hills in the west of the island, where they encountered friendly Irish settlers. The two peoples mingled and called themselves Cymri, which means fellow countrymen; they called their land Cymru. Nonetheless, they became better known by the name given to them by the Anglo-Saxons: Wealhas, which means foreigners.

The Welsh, as they came to be known, were Christianized in the 6th century. They persistently defended their land against the Anglo-Saxons and challenged the authority of the powerful King Offa of Mercia in a series of conflicts between 760 and 796. The first recorded king of Wales was Rhodri Mawr, who was otherwise known as Roderick the Great. Ruling from his seat in Anglesey, he drove off the raids of Norman pirates, who were the descendants of Viking raiders. Following his death in 893, his realm was divided among his three sons: Anarawd became king of North Wales; Cadalh became king of South Wales, and Mervyn became king of Mid-Wales.

Gruffydd ap Llywelyn united all Wales under his leadership, despite the opposition of the princes of the south. He allied himself with Ælfgar, an outlawed Anglo-Saxon earl, and they invaded England in 1055. However, Gruffydd's ambitions were finally ended after a successful military campaign when he was slain in 1063, by the forces of Earl Harold Godwinson, who later became King Harold II of England.

The Anglo-Saxon forces of Harold II were defeated by the army of Duke William of Normandy at the Battle of Hastings in 1066. The Norman Conquest marked a new era in the history of England: new cultural, ecclesiastical, and commercial links were established with the continent; the feudal system was introduced; and the Norman aristocracy displaced the Old Anglo-Saxon thegns. Although the new rulers of England claimed Wales as part of their dominion, the Welsh continued to defiantly maintain their independence, just as they had done with the Anglo-Saxons. William I, unable to subdue Wales, appointed earls to control the Welsh marches.

A brief conquest of North Wales by the Normans was decisively expelled in 1094, but by the end of the reign of Henry I in 1135, South Wales was practically an Anglo-Norman province. However, the Welsh revolted during the anarchic period following the death of Henry I and the accession of Stephen I, and freed all of Wales from English rule, with the exception of Pembroke. Two great princes emerged in Wales at this time: Owain of Gwynedd led in the north and Rhys ap Gruffyd led in the south. Henry II forced these princes to render homage to him in 1157, but they threw off the English yoke and freed Wales once again in 1165. The Welsh made masterful use of guerrilla tactics, making quick, effective thrusts before retreating to their bleak mountain homes to plan their next raid. It is a testimony to the indomitable fighting spirit of the Welsh that there are more castles, or ruins of castles, per square mile in Wales than anywhere else in the world.

Frustrated by their failure to subdue Wales, the discouraged earls of the marches turned their attention to the subjugation of Ireland instead, where they proved more successful. It was Richard de Clare, the Earl of Pembroke, who attained the conquest of Ireland during the Strongbow Invasion of 1172. Many Cambro-Norman settlers subsequently migrated from Wales to Ireland.

Llewellyn ap Gruffydd, the sovereign of most of Wales, scored a decisive victory over the English in 1267, and was acknowledged as prince of Wales by King Henry III. However, war erupted again in 1275, and two years later, Llewellyn was forced to accept peace terms dictating that the rulership of Wales would pass to the English Crown upon his death. Rebellion broke out once again in 1282 when Llewellyn's brother David seized Hawarden Castle and rode through Wales calling for revolt. All free Wales rose up in answer to his call.

However, Llewyllyn was decisively defeated this time and he was slain by the forces of Edward I in 1283; Shortly thereafter, the Statute of Rhuddan united Wales to England and divided it into counties. The king's son Edward II became prince of Wales in 1301. Nevertheless, revolts against English rule continued, notably under Owen Glendower, whose uprising against Henry IV lasted from 1400 to 1409.

Relations between Wales and England took a new direction during the late 15th century. The Tudors were a Welsh dynasty and fought on behalf of the House of Lancaster in the Wars of the Roses. One member of this house ascended the throne of England in 1485 as King Henry VII. Wales was brought into a legal and administrative union with England by his son King Henry VIII between 1534 and 1536. However, many Welsh continued to remain bitterly opposed to this union, and a powerful nationalist movement continues to quietly battle for independence to this very day.