§ Of the Coming of Men into the West The Silmarillion

In this way it came to pass that the Edain dwelt in the lands of the Eldar, some here, some there, some wandering, some settled in kindreds or small peoples; and the most part of them soon learned the Grey-elven tongue, both as a common speech among themselves and because many were eager to learn the lore of the Elves. But after a time the Elf-kings, seeing that it was not good for Elves and Men to dwell mingled together without order, and that Men needed lords of their own kind, set regions apart where Men could live their own lives, and appointed chieftains to hold these lands freely. They were the allies of the Eldar in war, but marched under their own leaders. Yet many of the Edain had delight in the friendship of the Elves, and dwelt among them for so long as they had leave; and the young men often took service for a time in the hosts of the kings.