Prior to the Tudor conquest of Ireland in the 16th century, Ireland was a "patchwork" of kin-based territories and kingdoms known as "túath."
The basic political and jurisdictional unit of Ireland, each túath was a self contained unit, with its own assembly, courts system and defence force. Túath, which means "the people", "country, territory", or "tribe, tribal homeland", observed complex relations with other such grounds throughout the country, occasionally forming confederations based on blood ties for mutual defence.
No one was stuck or bound to a given túath, either because of kingship or of geographical location. Individual members were free to secede from a túath and join a competing túath. Warfare between the territories was common.
Typically consisting of 6000-9000 people, the túath that observed their own internal hierarchies. Those further up the hierarchy had more privileges, wealth and power than those further down. The most powerful figure in the tribe was the rí, meaning king, from Latin rex, meaning “to stretch out straight,” and conveys similar meanings to the English word "regulate."
The rí was responsible for leading cattle raids against the neighbours, protecting his túath from attack, and enforcing Brehon law, an ancient Irish legal code that was transferred orally. Brehon law allowed women to own property. Additionally, archaeological discoveries indicate that women could achieve high status and power, and participated in warfare and kingship.
Within each túath, was an association of "fine", meaning family, that were ruled by a chieftain named a toísech (modern taoiseach). Representatives from each fine these formed a "derbfine" that would advise the rí and manage questions like property and inheritance.
They were assisted by the aosdána, a group of poets, druids and ocacles. The poets, or filí (seer, one who sees) was a class of magician, lawgiver, judge, counsellor to the chief, and poet, that could predict the future and perform incantations, as well as deliver curses.
Below that was a class of professionals such as physicians, and skilled craftsmen. Below that were freemen who owned land and cattle. Then there was freemen who did not own land or cattle, or who owned very little, and finally the lowest level of society was the unfree, which included serfs and slaves. There were also warrior bands known as the fianna that typically lived apart from society.
Unlike the caste system, these social structures were unfixed, and people could rise or descend in rank. Interestingly, the laws and rule of a túath did not extend beyond their own boundaries. However, they formed an interlocking system of tribal relations throughout the country.
For example, several túatha formed a mór túath, which was ruled by a rí mór túath or ruirí (overking). Several mór túatha formed a cóiced (province), which was ruled by a rí cóicid or rí ruirech (provincial king).
Although there was no central government, a number of local, regional and national assemblies were held, such as a gathering of the druids, kings, and chieftains on the Hill of Tara every third Samhain (halloween). There was also óenach, regional gatherings that were open to everyone. The main purpose of the óenach was to propagate and reaffirm the laws, which were read aloud in the gathering and any changes discussed and explained to those present.
There were further assemblies within each túath. These were the cuirmtig, which was open to all túath members, and the dal, which was open only to túath leaders.
While in the early Middle Ages the túatha was the main political unit, over time the túatha were subsumed into bigger conglomerate territories and became less important politically. Before the 8th century overkingdoms, or mór túatha, had begun to replace the túatha as the basic sociopolitical unit. From 1536, Henry VIII decided to conquer Ireland and bring it under English control.
Over the course of ancient Irish history, there is said to have instances of High Kings, that depicted Ireland as a unified political body in which rí reigned over an entire country of túath. However, modern historians believe this scheme is artificial, constructed in the 8th century to justify the current status of politically powerful groups by projecting it back into the remote past.