Comic Seikokugun Ryuuden

Dumashion, the second prince of the Ishkâk country, is accused of the murder of his father and his older brother. Behind this case is a plot orchestrated by the neighbouring kingdom of Nakâda. Now considered persona non grata, Dumashion has only one goal: to prove his worth and regain control of his homeland. He will be aided in his quest by a handful of colourful allies, as well as by mech-armor, those super-powerful robots capable of decimating entire armies.

(Source: Mangas.io, translated)