On the ÑoldorEdit
The Valar placed a ban on the rebelling Ñoldor who followed Fëanor to Middle-earth in pursuit of Morgoth and the Silmarils he stole. The ban came into effect after the Prophecy of the North was delivered as the Ñoldorin host traveled up through Araman, after it became known that Fëanor, with the support of a host led by Fingon, killed the people of Alqualondë to get their ships. The ban fell on the House of Fëanor, the House of Fingolfin, and those members of the House of Finarfin who did not repent their rebellion and turn back with Finarfin. During this time, the Valar hid Aman by meshing the sea around Tol Eressëa and Eldamar with a bewildering shadow and set the Enchanted Isles to ensnare any that set foot upon them. The ban ended after the War of Wrath when the Valar forgave the remaining Ñoldor. Of the leaders who had led the Noldor into exile only Galadriel chose to remain, having wed Celeborn.
On the NúmenóreansEdit
After the founding of Númenor, the Númenóreans were forbidden by the Valar from sailing so far westward that Númenor was no longer visible, for fear that they would come upon the Undying Lands, to which Men could not come. Over time the Númenóreans came to resent the Ban and to rebel against their authority, begrudging their mortality and seeking the everlasting life that they believed was denied them. Instead, in compensation, they looked eastwards towards the mainland of Middle-earth and established many colonies along its coasts. Initially this expansion was good and the Númenóreans came as teachers, but over many generations later they became conquerors and tyrants. Soon the Númenóreans came to rule a great maritime empire without rival. Few (the "Faithful") remained loyal to the Valar and friendly to the Elves.