Plegia is the hostile nation that attacks Ylisse in Fire Emblem Awakening.
Awakening takes place in a land descended from the settings of earlier Archanea games. In its present era, the Halidom of Ylisse is threatened by its neighboring kingdom, Plegia. Plegia follows the worship of the Fell Dragon Grima, while Ylisse venerates the Divine Dragon Naga, creating a deep religious and political divide.
The hostility also has a recent historical cause. Fifteen years before the game begins, Ylisse’s previous Exalt waged a religious war against Plegia. The conflict damaged both nations and left lasting resentment. Although Exalt Emmeryn later pursues peace, Plegian forces under King Gangrel resume aggression and attack Ylisse.
The other options belong to different Fire Emblem settings. Grado is associated with The Sacred Stones, Daein with the Tellius games, and Nohr with Fates. Plegia’s role is especially important because the early campaign against it introduces Chrom, Robin, the Shepherds, and the game’s central political conflict.