In the power vacuum left when the Romans abandoned the British Isles, many small Celtic kingdoms sprang up, opposing each other continuously. Germanic peoples, brought to Britain by the Romans as mercenaries, quickly alarmed their countrymen back home, and before the Celts had managed to unify, the Germans (particularly Saxons, Angles, Jutes and Frisians) were all over England. The Celts were forced back to Cornwall, Scotland and Wales.
Wales contained several small kingdoms, although there were a few rulers, such as Rhodri the Great, who controlled nearly all of Wales. The separate kingdoms, with the help of the mountainous terrain, managed to hold the Germans at bay. The English, as they were soon known, managed to conquer Cornwall, but gave up trying to conquer Wales. All they wanted was to control it: the English king Offa built a long earthen wall, still visible today, supposedly to show where England ended and Wales began.
When the Normans invaded England in 1066, a new invasion of Wales was started. This time it consisted mostly of freebooters and settlers, primarily from Normandy and Flanders. They settled mostly in the south of Wales, slowly working their way from Gloucestershire to Pembrokeshire, where the important St. David's Cathedral was (and is) located. The Welsh lords could do little, as openly fighting the Normans would result in war with England; yet allowing the Normans to settle would erode their own powers.
Although the Normans had gained a foothold in south Wales, it was tenuous at best. In the north, things fared better, and the Normans drove out the king of Gwynedd. Welsh resistance was centred on the western part of the land. In the 12th century, the situation reversed. The lords of Gwynedd returned from exile in Ireland and pushed out the Normans in very little time, while in the south the Welsh were fighting a losing battle against royal power. Soon, the lords of the south were of little importance, while the princes of Gwynedd would become the dominant figures in Welsh politics.
The Welsh ways of warfare were very different from those of the English; they used hit-and-run raids to discourage English morale, attacking supplies and lone troops. Their guerrilla warfare was merciless, and relied mostly on their infamous longbows and javelins.
There was only one answer to this: building impregnable castles all over Wales to cement royal power. The Welsh Wars, as they are called, saw Llywelyn II, prince of Gwynedd, pitted against King Edward I. At first, the Welsh were fighting quite successfully against the English, but when Llywelyn II was killed in a skirmish, the Welsh cause collapsed. The remaining Welsh freedom fighters were captured and executed for treason.
Wales was conquered in 1283, but held on to its identity. The English adopted the famous Welsh weapon, the longbow, and for centuries to come the Welsh would find profession mostly in English - later British - armies.