First Age followed by Second Age
Years of the Sun
The Years of the Sun were the last of the three great time-periods of Arda.  They began with the first sunrise in conjunction with the return of the Noldor to Middle-earth, and last until the present day. The Years of the Sun began towards the end of the First Age of the Children of Ilúvatar and continued through the Second, Third, and part of the Fourth in Tolkien's stories. Tolkien estimated that modern times would correspond to the sixth or seventh age.Second Age
The Second Age is characterized by the establishment and flourishing of Númenor, the rise of Sauron in Middle-earth, the creation of the Rings of Power and the Ringwraiths, and the early wars of the Rings between Sauron and the Elves. It ended with Sauron's defeat by the Last Alliance of Elves and Men.At the start of the Second Age, the Men who had remained faithful were given the island of Númenor, in the middle of the Great Sea, and there they established a powerful kingdom. The White Tree of Númenor was planted in the King's city of Armenelos; and it was said that while that tree stood in the King's courtyard, the reign of Númenor would endure. The Elves were granted pardon for the sins of Fëanor, and were allowed to return home to the Undying Lands. The Númenóreans became great seafarers, and were learned, wise, and had a lifespan beyond other men. At first, they honored the Ban of the Valar, never sailing into the Undying Lands. They went east to Middle-earth and taught the men living there valuable skills. After a time, they became jealous of the Elves for their immortality. Sauron, Morgoth's chief servant, was still active. As Annatar, in disguise he taught the Elves of Eregion the craft of creating Rings of Power. Seven Rings were made for the Dwarves, while Nine were made for Men who later became known as the Ringwraiths. He built a stronghold called Barad-dûr and secretly forged the One Ring in the fires of Mount Doom to control the other rings and their bearers. Celebrimbor, a grandson of Fëanor, forged three mighty rings on his own: Vilya, possessed first by the Elven king Gil-galad, then by Elrond; Nenya, wielded by Galadriel; and Narya, given by Celebrimbor to Círdan, who gave it to Gandalf.As soon as Sauron put on the One Ring, the Elves realized that they had been betrayed and removed the Three (Sauron eventually obtained the Seven and the Nine. While he was unable to suborn the Dwarf ringbearers, he had more success with the Men who bore the Nine; they became the Nazgûl or Ringwraiths). Sauron then made war on the elves and nearly destroyed them utterly during the Dark Years, but when it seemed defeat was imminent, the Númenóreans joined the battle and completely crushed the forces of Sauron. Sauron never forgot the ruin brought on his armies by the Númenóreans, and made it his goal to destroy them.Towards the end of the age, the Númenóreans became increasingly haughty. Now they sought to dominate other men and to establish kingdoms. Centuries after Tar-Minastir's engagement, when Sauron had largely recovered, Ar-Pharazôn, the last and most powerful of the Kings of Númenor, humbled Sauron – his armies deserting in the face of Númenor's might – and brought him to Númenor as a hostage, although this was Sauron's goal. At this time still beautiful in appearance, Sauron gained Ar-Pharazôn's trust and became high priest in the cult of Melkor. At this time, the Faithful (who still worshipped the one god, Eru Ilúvatar), were persecuted openly by those called the King's Men, and were sacrificed in the name of Melkor. Eventually, Sauron convinced Ar-Pharazôn to invade Aman, promising him that he would thus obtain immortality. Amandil, chief of the Faithful, sailed westward to warn the Valar. His son Elendil and grandsons Isildur and Anárion prepared to flee eastwards, taking with them a seedling of the White Tree of Númenor before Sauron destroyed it, and the palantíri, gifts of the elves. When the King's forces set foot on Aman, the Valar laid down their guardianship of the world and called on Ilúvatar to intervene.
The world was changed into a sphere and the continent of Aman was removed, although a sailing route from Middle-earth to Aman, accessible to the Elves but not to mortals, persisted. Númenor was utterly destroyed, as was the fair body of Sauron; however, his spirit returned to Mordor, where he again took up the One Ring, and gathered his strength once more. Elendil, his sons and the remainder of the Faithful sailed to Middle-earth, where they founded the realms in exile of Gondor and Arnor.
Sauron arose again and challenged them. The Elves allied with Men to form the Last Alliance of Elves and Men. For seven years, the Alliance laid siege to Barad-dûr, until at last Sauron himself entered the field. He slew Elendil, High King of Gondor and Arnor, and Gil-galad, the last High King of the Noldor in Middle-earth. However, Isildur took up the hilt of Narsil, his father's shattered sword, and cut the One Ring from Sauron's hand. Sauron was defeated, but not utterly destroyed. Afterward, Isildur ignored the counsel of Elrond, and rather than destroy the One Ring in the fires of Mount Doom, he kept it as weregild for his dead father. But the Ring betrayed him and slipped from his finger as he was escaping from an Orc ambush at the Gladden Fields. Isildur was killed by an orc arrow, and the Ring was lost in the Anduin River.