The Washing was a period of Faelish history marked by the large-scale settlement of Faeland by Celtic peoples, mostly from the Insular territories. The settlement resulted in the breakdown of large states and a return to tribal chiefdoms before and eventual re-emergence of Faelo-Celtic petty kingdoms, as well as a fusion of local and immigrant cultures. This period also marks the introduction of horses onto the isles as well as the technology of the chariot.
According to a well-established theory, prior to becoming known to the Faelish world, Gaelic speaking tribes were part of the many confederacies of the eastern Atlantic. The peoples who invaded Faeland arrived seemingly "from the sea" when the westward movement of outlier tribes in their homelands in the 6th and 5th centuries BCE triggered their transoceanic migration to the Faelish Isles. The first arrival for which we have any solid archaeological evidence is at Çafhilen dated to the 420's BCE. From this point the newcomers dispersed up the river valleys -particularly the Verdan- and down into Çeniteq lands and finally across the mountains into Hesion and beyond the Glaeken Fault.
The ethnographic result was a patchwork of culturally-hybridized tribes woven together by a complex political system which was never highly centralized at any point in time. The fundamental unit of Washing-era society was the clan, which itself consisted of one or more families. Each clan had a council of elders, and initially a chieftain-like leader. The regional ethnic groups or tribes (as the Romans later called them) were organized into larger alliances called Deins (pr. "danes"). These defensive groupings would coalesce into kingdoms and petty states by the middle ages as borders and relations stabilized during the period of Roman contact and after the latter's collapse.
By far the most significant social and political result of the sea-comers' arrival was the collapse of the Bhiriduxhiann Arniho system which allowed a fusional ethno-cultural group to emerge in the central Midlands . As the revolutionary works of Moadh Eehvscu proliferated throughout the isles, Axatut Maxume took place leaving power vacuums whereby the immigrants found welcome among the local peoples. It was this well-timed injection of newcomers which re-invigorated Alntlöán and led to the creation of the first historical instance of a Sasarg/Xanpai diarchy. Known to history as the "Kingdom of Faeland" this polity would endure until itself fusing with the Alnish state in the 10th century CE.