The country of Georgia has known a rich military history, both as a battlefield of empires and as an independent political and military power. The strategic significance and natural wealth of its territory made it the target of many invasions, and the country's independence was preserved against multiple enemies by a succession of states. Before the unification of the country by the Bagrationi dynasty in the 10th century, several Georgian states, such as Iberia and Colchis had managed to subsist between the Roman empire (later Byzantine Empire in the West) and the Sassanid Empire (later replaced by the Umayyad and Abbasid Caliphates). Between the 11th and 15th centuries, the Kingdom of Georgia was a major regional power, which withstood invasions by the Great Seljuk Empire, Mongol Empire,