Which country is featured in Ace Combat 5: The Unsung War?

The country featured in Ace Combat 5: The Unsung War is Osea. Osea is the main focus of the game's storyline and campaign, as players take on the role of an Osean pilot. The game revolves around the conflict between Osea and its rival neighboring country, Yuktobania, with the player's mission being to defend Osea against various enemy forces and ultimately bring about peace. Osea's involvement and its strategic importance to the game's narrative make it the prominently featured country in Ace Combat 5: The Unsung War.