The game takes place in a fantasy medieval kingdom of Thorin ruled by the benevolent King Galamar. The game begins with Galamar barely escaping a bloody coup by his younger brother Valadorn, who has taken control of the kingdom and declared a hunt on his brother. Galamar has few troops with him, and he is constantly being attacked by Valadorn's Red Legion. In the first part of the campaign, Galamar has to gather allies in order to strike back at his brother. These allies include the Lizard King, the Wizards of the Grey Tower, the Wyverns captured by Valadorn's forces, etc. Once Galamar defeats Valadorn for the last time, he realizes that his brother was under demonic control. The game ends with a cliffhanger.
Source: Wikipedia, "Ancient Empires (mobile game)", available under the CC-BY-SA License.