During the Third Age, the term was applied to those tribes and kingdoms of Men living beyond the Sea of Rhûn, who were allied with Sauron and frequently attacked Gondor.
The first Easterling attacks were in the late 5th century of the Third Age and were repelled by King Ostoher and his son Rómendacil I. Later King Turambar fought wars of conquest against the Easterlings, extending Gondor's borders to the Sea of Rhûn.