The great island kingdom founded by the Edain in Tolkien’s legendarium is Númenor.
Númenor, also called Westernesse, was created by the Valar for the Edain who had aided the Elves during the wars against Morgoth in the First Age. The island lay in the Great Sea between Middle-earth and Aman. Elros, the half-elven brother of Elrond, became its first king and chose the fate of Men.
Númenórean civilization grew powerful, long-lived, and skilled in seafaring. Over time, however, many of its people became jealous of the immortality associated with the Elves and feared death. This change in attitude contributed to the kingdom’s downfall under King Ar-Pharazôn.
Númenor was destroyed when its king attempted to challenge the divine order and sail against Aman. Survivors founded the kingdoms of Gondor and Arnor in Middle-earth, linking Númenor directly to the later history of Aragorn and the Dúnedain.