Erusea, officially the Kingdom of Erusea, is a large nation located on the westernmost part of the Usean continent. Erusea shares its border with San Salvacion and at least one other nation. Its capital, Farbanti, is located on the coast of Usea's westernmost peninsula near the Spring Sea.

Formerly the Federal Republic of Erusea or Erusean Republic , the nation is known for its industrialism, militarism, and advancements in engineering and aeronautic technologies. It was severely affected by the impact of Ulysses 1994XF04 in 1999. By mid-2003, tensions between Erusea and the other Usean nations escalated into open war, in which Erusea was soundly defeated.

The nation was restored into a kingdom sometime afterward. Following the construction of the International Space Elevator in Axel Bay, Erusea occupied the space elevator and declared war on the Osean Federation.

Erusea was the antagonist country in Ace Combat 04: Shattered Skies, and made a brief appearance in Arcade Mode in Ace Combat 5: The Unsung War. It once again acted as an antagonist in Ace Combat 7: Skies Unknown.