Tuatha De Danann Tribes
The De Danann people arrived after the Firbolgs, and were to force the Firbolgs into partial serfdom. The Tuatha De Danann established Tara on the Boyne Valley, the ritual inaugaration and burial place for the ancient Kings of Ireland.
Source: various
In a famed battle at Southern Moytura (on the Mayo-Galway border) it was that the Tuatha De Danann met and overthrew the Firbolgs. The Firbolgs noted King, Eochaid was slain in this great battle, but the De Danann King, Nuada, had his hand cut off by a great warrior of the Firbolgs named Sreng. The battle raged for four days. So bravely had the Firbolgs fought, and so sorely exhausted the De Dannann, that the latter, to end the battle, gladly left to the Firbolgs, that quarter of the Island wherein they fought, the province now called Connaught. And the bloody contest was over.
Source: http://www.vretail.com/history.htm