Netheril

Netheril was the biggest kingdom ever recorder in the history of the Forgotten Realms. It lasted for almost 3.500 years and spanned the entire continent of Faerûn.
The kingdom was so rapidly expanding, that the humans who founded it ran out of space and started deploying magic to create floating islands in the sky for their kingdom to grow.
However, the human ambition grew so strong, that they even challenged the gods.
The empire fell after the events following Karsus's Folly.