During the War of the Ring Edit
In the north, the realm of Arnor had fallen into troubled times. It broke into three separate kingdoms, and in time these too were lost, so that the Dúnedain of the North-kingdom of Elendil were reduced to a wandering people led by a Chieftain. Nonetheless, they were able to maintain Isildur's line in unbroken descent. However this failed in Gondor, and Eärnur was lost, without heirs, in TA 2050. Gondor's rule was taken up by the Stewards.
There were two attempts to reunite the kingdoms. The first of these occurred when Arvedui of Arthedain claimed the High Kingship of the Two Kingdoms. His claim was rejected by Steward Pelendur and the Council of Gondor, who elected to maintain their independence.
More than a thousand years later, after the War of the Ring, Arvedui's direct descendant Aragorn came forward to make the same claim. This time, the people of Gondor accepted a High King, and the Two Kingdoms were reunited at last.
Aragorn II ruled from Minas Tirith, which became even greater and more beautiful than it was in the first days after its construction, but he travelled throughout his wide lands, and rebuilt Annuminas. When he went north he would rule from there. The Shire was an exception to this, and though it lay within the Reunited Kingdom, Aragorn made a law that Men should not enter it, a law that he observed himself.
After Aragorn's death, his son Eldarion took up the High Kingship, and the Reunited Kingdom endured for many years under the new King and his descendants.