In Fullmetal Alchemist: Brotherhood, both the best and worst of humanity were on full display, and for Major Alex Louis Armstrong, he was firmly on the side of healing and compassion, not war. Despite his strength, his muscles were not meant for murder. More than once, Alex was berated for his unwarlike ways, like from King Bradley (Wrath) and his big sister, Major-General Olivier Armstrong. However, unlike Wrath, Olivier appreciated the compassionate side of her brother, and Alex represented what the Amestris military needed the most: the wisdom to not engage in hateful violence.
Many plot twists in Fullmetal Alchemist were grim ones, and most of them could be traced back to Father's grand plan to sacrifice humanity to become a godlike being. The entire nation of Amestris was founded with Father's plan in mind, and for centuries, this nation's history was defined by wars, skirmishes and genocide, among other violent events.
The most recent example was the Ishval Civil War, which Alex took part in. In a manner of speaking, neither side "won" this war, especially not the Ishvalans. The only party to benefit from this was Father, who needed a scene of massive carnage to fuel his giant transmutation circle.
The Amestrians were even cruel to themselves, and for a time, Alex was not privy to this at all. The military and government conducted unethical experiments on prisoners and test subjects, turning Ishvalans and researchers into Philosopher's Stones. Other prisoners were transmuted into armored bodies, not unlike Alphonse Elric.
In this nation, everything was intended to become a weapon of war, and schemes, plots and selfish ambition ruled the military. Many officers were on Father's and Wrath's side, being the "chosen ones" who would supposedly gain immortality. Then there's Colonel Roy Mustang, a scheming anti-hero, and Olivier, who saw everything as a potential weapon against Drachma. Meanwhile, Alex bucked these trends and never gave into hate, malice or despair.
Few members of the military opposed this general trend, with Maes Hughes being a rare exception, but Alex was an even finer example. Alex was born into a noble family, and though he took pride in that, he's not the type to rest on laurels. Alex repeatedly showed his humble side, knowing his place in the military and speaking highly of his family traditions, but not himself. Plus, to Alex, defending peace and justice were the true reasons to engage in violence, not glory. Otherwise, war was senseless slaughter, and Alex refused to subscribe to Amestris' deadly ways.
It took strength to not act on feelings of anger or vengeance, something that his sister and Wrath wouldn't appreciate nearly as much. For example, Alex took part in the raid on Greed's hideout, and his opponent was Roa, a chimera who fought in Ishval. Roa and his fellow chimeras were merely doing what they must to survive, and only Wrath's "kill them all" order made them enemies. Alex held back in their duel, recognizing Roa as more of a peer than an enemy, something Wrath berated him for.
Most of all, Alex broke down during the Ishval Civil War, recognizing it as pointless brutality, and he refused to uphold it, so he was branded a coward. In reality, he had the courage to defy the senseless carnage and stand up for what was right, something Edward would appreciate.
Meanwhile, Alex fought bravely against the homunculi, who were not innocent victims, and he took on the monstrous Sloth alongside Olivier. They fought well, but Sig and Izumi Curtis had to help, and Alex graciously accepted the help and finally took Sloth down. Cooperation and trust triumphed over malice and wrath, and that's an example the rest of the military could stand to follow. Misused strength is no strength at all, and alchemy doesn't have to be a weapon, and no one understood this as well as Alex.