His first target was the realm of Rhudaur. It was around this time that the Witch-king established himself in Angmar (thus gaining his title) and began to launch attacks against the nearby kingdom of Arnor, which had fractured into three smaller kingdoms. The Nazgûl re-emerged around 1300 of the Third Age, as Sauron at long last began to take shape after his defeat at the hands of the Last Alliance.
Though no longer able to maintain physical form, just as Sauron was after losing the One Ring, both the Nazgûl and Sauron were able to endure as long as the Ring survived. They were temporarily dispersed after Sauron's downfall in SA 3434 in the War of the Last Alliance. Despite their great power and position as instruments of Sauron's will, not much is known of their activities during the Second Age. The Nine were first observed around 2251 of the Second Age, and soon became Sauron's primary servants. Only two of the Nine were ever named: the Witch-king of Angmar and Khamûl the Easterling. Three of the Ringwraiths may have been among the first and most powerful Númenóreans to be corrupted by Sauron, a thousand years before the Downfall: they revered Sauron, and became ensnared in his designs because of their lust for power or knowledge. Their lives and their powers became bound to Sauron's via the One Ring as Sauron grew or diminished, so too did the Nazgûl. The Rings eventually rendered their bearers invisible to all but those who could see into the wraith world, and enslaved them to the will of Sauron. These Nine used the rings to achieve great power, wealth, and prestige in life, but as time passed the Rings continued to exert a corrupting influence. Sauron succeeded in corrupting the powerful Nine through his dominance over the rings. He gave nine of them to great lords and warriors of Men, including three Númenóreans, and one Easterling king. These were locked away in one of the safes of Eregion, but all were captured by Sauron. Nineteen Rings of Power were made in Eregion, forged by Celebrimbor.
Kings of Men with their Rings of Power, as seen in The Lord of the Rings: The Fellowship of the Ring 7.1 The Lord of the Rings Trading Card Game.1.3.1 Battle of the Morannon and Defeat.