From "A New History of Ireland," edited by Moody, Martin & Byrne, vol 3, ISBN 0-19-821739-0, 1976, pp. 6-7: The north-western part of County Wicklow was more or less [in 1534] a no-man's land until the 8th Earl of Kildare bought out surviving but nominal medieval land-titles, apparently from the Dunboyne Butlers, to give to his sons by his second marriage. . . Along the northern border of the present County Wexford was another no-man's-land, the title to the larger part of which had been acquired by the 8th earl of Kildare, who thereupon took it over from the Irish occupants. [See Kildare Rental Book (B.M., Harl. MS 3756), ff 8 5v[erso?]-6 compiled by John T Gilbert in Nat'l Library of Ireland, MS 10, 203 (4).]

The power of the House of Kildare reached its zenith during the time of Garret Mór, the 8th Earl, henceforth known as the "Great Earl".  He established a sovereignty which lasted until 1534 and the rebellion of his grandson, Silken Thomas.  He fought Irish and English alike, and his hostings which brought him as far as Connaught and Ulster, illustrate his authority and the extent of his power.  Guns, seen in Ireland for the first time in 1489, were used by him with resounding success.  During his time the wealth and lands of the Kildares were extensive, whilst his learning was reflected in his comprehensive library of English, French, Latin and Irish books housed at Maynooth.
The Great Earl was a Yorkist supporter, and, following the victory of the Lancastrians in the War of the Roses, he supported the claims of the Pretenders to the English throne, Lambert Simnel and Perkin Warbeck.  Although arrested for treason Garret Mór was restored to power by Henry VII in 1496 and he remained "Uncrowned King" of Ireland until his death in 1513.