Political peace and theology do not always go hand in hand. We can still see the problem lived out today in such martyrs as Archbishop Romero and in the Seventh Century in the likes of Martin.
The power of the pope was increasing and Martin's carrying out of the Lateran Council in 649 shows the boldness of his action against an Emperor whose edict was designed to silence discussion and promote political quietude.
But it is not the histo-political aspect of this man that we want to concentrate on but the adherence to the Truth that drove him, even as an old man, to defy and clarify bad theology - and to pay for it with his life. The importance of Jesus being both God and human is so vital to the Truth of Christianity that to lessen or deny any aspect of it removes the foundation of the whole tower. In the Truth, the tower stands tall and straight, firmly rooted against wind, rain, heat, and cold. Revelation founds the Faith and negates the need for us to explain the mystery. To wiggle the foundation does not show the weakness of the foundation of Revelation but of our own human weakness and hubris and shows the necessity of retaining all of Revelation as a solid foundation. Martin reminds us to cling to and teach only the Truth.
Two last things: Martin was actually an Easterner, not a Roman. After his papacy, the West tended to elect only Westerners and the East only appointed Easterners. The divide continued to expand until its failure three centuries later. Second, Martin is also the last pope that we consider a martyr, which of course speaks to the deaths of many of the popes to come after him and the causes of their deaths, usually also for political reasons, if you understand my meanings.
If anyone who indubitably has professed and also understands those (teachings) which the wicked heretics suggest, through vain impudence says that these are teachings of piety, which the investigators and ministers of the Word have handed down from the beginning, that is to say, the five holy and universal Synods, certainly calumniating [maligning] the holy Fathers themselves and the five holy Synods mentioned, in the deception of the simple, or in the acceptance of their own impious treachery, let such a person be condemned.
If anyone according to the wicked heretics in any manner whatsoever, by any word whatsoever, or at any time or place whatsoever illicitly removing the bounds which the holy Fathers of the Catholic Church have rather firmly established [Proverbs 22:28], that is, the five holy and universal Synods, in order rashly to seek for novelties and expositions of another faith; or books, or letters, or writings, or subscriptions, or false testimonies, or synods, or records of deeds, or vain ordinations unknown to ecclesiastical rule; or unsuitable and irrational tenures of place; and briefly, if it is customary for the most impious heretics to do anything else, (if anyone) through diabolical operation crookedly and cunningly acts contrary to the pious preachings of the orthodox (teachers) of the Catholic Church, that is to say, its paternal and synodal proclamations, to the destruction of the most sincere confession unto the Lord our God, and persists without repentance unto the end impiously doing these things, let such a person be condemned forever,and let all the people say: so be it, so be it [Psalm 105:48].
-- Lateran Council, Canon 19-20