After the war, some of the Noldorin Exiles sailed away from Middle-earth to return to their homes in Eldamar, near to the shores of Valinor. But many remained in Middle-earth, setting up new realms called Lindon and Eregion and Lothlórien. The Valar rewarded the Edain by granting them the great island of Elenna, between Middle-earth and Eldamar, but they placed upon them the Ban of the Valar, forbidding the ships of Men to travel west toward Eldamar and Valinor. The Men established the kingdom of Númenor there that grew mighty on its sea-borne trade. They became known as the Dúnedain, or Men of the West. Those Men who had remained in Middle-earth were known as the Uialedain, or Men of the Twilight, and they formed petty tribes, often at war with one another.
As the power and wealth of Númenor increased, its kings grew proud and came to resent the Ban of the Valar. The people of Númenor became divided, many sharing their king's envy of the immortality of the Elves and the Valar. But always a minority remained faithful to the Valar and maintained friendly relations with the Elves. The kings ceased to use the Elvish tongues and reverted to the ancient tongue of their ancestors, the Edain of Middle-earth. In the thirtieth century, King Ar-Adûnakhor persecuted the Faithful and they fled into the westernmost province of Andúnië where their party was strongest. Soon after this the use of the Elvish tongues was forbidden by royal decree.
In 3175 Tar-Palantír came to the throne and tried to end the division. He pardoned the Faithful, but feelings by this time were too high against them, and there was rebellion in the land. In 3255, Palantír died and the rebel leader, Palantír's nephew, seized the scepter and took the name Ar-Pharazôn. Palantír's heirs fled to Andúnië.
At this time a new evil arose in Middle-earth in the form of Sauron. He was a Maia, one of the lesser Ainur, and he had been Morgoth's chief lieutenant and student. In the mountain-ringed southeast portions of Middle-earth he had secretly built for himself the realm of Mordor, the Black Land, peopled by orcs, an evil race created by his master. He deceived Celebrimbor of Eregion into teaching him how he had made the Great Rings of Power, and he forged for himself the One Ring to absorb the powers of all the Great Rings. With this new weapon he rose against the Elves and the Uialedain, and he drove them back before the fury of his armies. The Elves were hard-pressed until Ar-Pharazôn in 3262 sent his mighty fleet to Middle-earth to intervene. The overwhelming might of the Númenorean fleet quickly prevailed, and Sauron was taken back to Númenor in chains. But over the years he gradually rose from captive to guest of the court to advisor, and finally to first minister. He fueled the pride and arrogance of the king and urged him to ever greater persecution of the Faithful; but Amandil, Lord of Andúnië, and his son Elendil steadfastly maintained their opposition to Pharazôn's policies. This was the troubled world into which Isildur was born.
Of Isildur's early life we know very little. He was born in 3289 Second Age in Dol Elros, the chief city of Andúnië. His father was Elendil, the Prince of Andúnië and the spiritual and political leader of the Party of the Faithful. In 3285, Elendil married Aldamirë, a woman of southern Númenor, and she gave him two sons, Isildur in 3289 and Anárion in 3296. Amandil was elderly by this time and the people rallied around the handsome and charismatic young prince Elendil, just as they would gather to his eldest son many years later. In 3310, the aging king Pharazôn, urged by Sauron, resolved to assail Valinor to acquire the immortality of the Valar for himself. He began building ships and engines of war to Sauron's designs. The Faithful tried to dissuade the lords and people of Númenor from their blasphemous course, but Pharazôn punished all dissent with death. A religious and patriotic fervor developed against the Faithful and Andúnië was isolated from the rest of the kingdom, an embattled fiefdom.
In 3319, the Great Armament sailed for Valinor. Elendil believed that all of Númenor would be destroyed when the Ban was broken, and he began preparing for a hasty evacuation. His father Amandil attempted to repeat Eärendil's feat by enlisting the aid of the Valar, but his expedition was never seen again. Pharazôn landed in Valinor and the Valar enforced their Ban by withdrawing their gift of the island of Elenna. The island crumbled and sank forever beneath the waves. Of the Great Armament, its hundreds of ships and thousands of men, no trace was ever found.
Elendil and his sons and hundreds of their followers escaped the destruction in a fleet of nine ships, taking with them the treasured relics of their ancient line: the Scepter of the Lords of Andúnië; the Ring of Barahir; a seedling of Nimloth, the White Tree; the nine Palantíri or seeing stones; and the great sword Narsil — all gifts of the Eldar to the Lords of Andúnië.
Isildur was a young man of thirty as he stood in the prow of his ship and watched the domes and towers of his homeland torn asunder and cast beneath the waves. The forlorn little fleet was borne away by a terrible storm and became separated. Elendil at last reached Mithlond, the Grey Havens of the Elves of Lindon, and was taken in by his friend Gil-galad, King of the Noldor. Later he was granted land east of Lindon and he and his people removed there. They founded a realm with its capital at Annúminas beside lake Nenuial, and named the land Arnor, the Royal Land.
Isildur and Anárion landed near to the one haven of the Faithful in Middle-earth, the port city of Pelargir near the mouth of the Great River Anduin. They began the ordering of a great realm along the Anduin. They built their capital Osgiliath, Citadel of the Stars, where the mountains drew close to the river on either side. The fair lands along the River became dotted with farms and vineyards and orchards and the rocky land soon began to yield its richness. They named their new land Gondor, the Land of Stone, and divided it into two provinces separated by the River; Ithilien on the east under Isildur, and Anórien on the west ruled by Anárion. Isildur built a fortress city high in a pass of the Ephel Dúath and named it Minas Ithil, the Tower of the Rising Moon. On the slopes of Mindolluin, the easternmost peak of the Ered Nimrais, Anárion built Minas Anor, the Tower of the Setting Sun. For many years Arnor and Gondor, the Realms in Exile, prospered and grew in power and wealth, and the Great North Road was busy with many travelers and wagons bearing produce and goods between the sister kingdoms. In 3409 Isildur married Vorondomë, daughter of the Captain of the Ships of Ithilien. She gave him four sons between 3412 and 3429: Elendur, Aratan, Ciryon, and Valandil.
The future looked very bright for the young lord Isildur: a fair land to rule; a beautiful and loving queen; a growing family; and the prospect of one day becoming King of the Realms in Exile and ruling the greatest kingdom in Middle-earth. Then in the autumn of 3429, disaster struck. A huge force of barbarians, trolls, orcs, and many other fell creatures swept over the mountains out of Mordor. They were led by Sauron, in a new and even more powerful form, dead and yet not dead. All had thought him killed in the fall of Númenor, but he had escaped with his hatred for the Dúnedain unabated. His savage hordes swept across Ithilien and besieged Minas Ithil. After a brief but bitter struggle, the gates were breached and the enemy spread through the city, destroying all in their path. The defenders formed a wedge around their families and drove desperately through their attackers, eventually reaching Osgiliath.