The continent of Tellius is the last remaining landmass in the world, inhabited by two distinct people. The Beorc, which are what amount to humans, wielding swords, shields, spells, and armor, and the Laguz, or the beast tribes, which fight with tooth and talon and claw, able to change from a humanoid form to a beast form depending on their species. The Beorc nations are those of Crimea, Begnion, and Daein. The Laguz nations are the Lion, Cat, and Tiger tribes of Gallia, the hawks of Phonecias, the ravens of Kilvas, the dragons of Goldoa, the herons of Serenes Forest, and the lost wolf tribes of the Desert of Death. (Map — http://images4.wikia.nocookie.net/fireemblem/images/9/93/Tellius_map.jpg)
There has always been some animosity between the Laguz and Beorc nations, but no outright war. That is, until the nation of Daein invaded its neighbor, Crimea, beginning what was known as the Mad Kings War. Ashnard, the king of Daein, desired the awakening of the dark goddess of Chaos, Yune, and the plunging of the world into destruction. He was stopped by a group of mercenaries at the head of a large army — the Greil Mercenaries led by General Ike, flying the banner of the lost royal heir to Crimea, Ellincia. Defeating the Mad King in Castle Crimea, the continent was returned to peace.
This peace did not last, as the nation of Begnion began to be taken over by the corrupt senators that incarcerated both the Apostle, Sanaki, and the Prime Minister, Sephiran. The Begnion Occupational Army in Daein began to visit atrocities upon the people — but again, a small group of people fought back. This time, it was the Dawn Brigade, led by the Silver-Haired Maiden, Micaiah. They defeated the occupation, and restored Daein to its people. Though, at the same time, the Begnion Central Army was deployed, against the nation of Gallia. War began to engulf the continent once more. Ike and the Greil Mercenaries were hired to assist the Laguz Alliance against Begnion, and they responded, fighting back the overwhelming army of Begnion. But all was not well — the constant fighting threatened to awaken Yune, and so the remaining herons released the goddess willingly — the only way to postpone the judgment of Ashera.
Yune turned out to not be the dark god she was spoken of, and instead was half of the goddess Ashunera. Her counterpart, Ashera, froze in stone all of the Laguz and Beorc, save for a few chosen champions. Ike, at the head of the chosen of Yune, entered the Tower of Remembrance, and with his friends, defeated the forces of Order, restoring the frozen people of Tellius, and restoring peace once more.