Understanding the Celts is understanding something that passed into shadow over two thousand years ago. The Celtic nations that emerged after the Roman evacuation of Britain were changed out of recognition from the Celts who had lived on the misty island of Britain six hundred years before.
Really I am going to be talking about the Celtic ideal. How far that ideal was from the truth is anybodies guess but just for now lets be generous in our judgements and imagine that the Celts lived up to their own ambitious ideals.
From the first century BC on wards money began to flow into Britain from trade with the Romans and other Mediterranean powers. We know that thePheonicians were trading with the tribes who lived in what is now Cornwall and Wales for tin and copper since time immemorial. Prehistoric mines inLlandudno in particular are testament to the commitment of prehistoric Britain to trade in resources. The Celts were not only exporting mineral wealth but also slaves. This indicates first that the population was larger than necessary for a subsistence survival, otherwise that slave labour would have been put to use in the slaver fields rather than being exported to the continent. Second it indicates that law and order was in decline, Britain was becoming a more dangerous place. From recent history in Africa we can see the impact of slavery, unstable society, increasing wealth and power of slavers and freebooters and new elites emerging from these freebooters.
We know from Tacitus that in prehistory the Celts had been ruled by kings and high kings but by the first century AD this had been replaced by a tribal system of chiefs, warlords and petty kings. As money had flowed into the country it created an egalitarian society diminishing the influence of the kings and creating a class of powerful chiefs, similar to the class structure in England during the War of the Roses. In both cases the country was dominated by powerful families who engaged in raiding each other, excessive symbolic demonstrations of power and social instability. The Celts in particular become devotes of the cult of the warrior and the cult of personality surrounding successful and powerful leaders. Violence, feuding, raiding and brutality were common, ritualized and fetishistic. Characters such as Culhwch are terrifying characters who engage in terrible acts of psyching up before desending on his enemies and killing everyone regardless of age, sex or class. Such characters surround themselves with retinues and warbands who venerate the hero and recieve all the benefits of being in cortege.
First century AD Britain was a very sexy place to live, despite being very dangerous for anyone not under the protection of the feuding chiefs. This proved extremely advantagous to the Romans who knew very well that they would have a hard time in Britain if they could work together. During the Boadicea revolt the celts were successful when they worked together and were defeated when they began to squabble.