A Real Man is a Patriot
A true man loves his country, and is willing to stand by it and fight for it.
There is a certain manliness about patriotism. A soldier's duty to fight and die for one's nation is among the manliest things on the planet, and even when one isn't a soldier, love of one's country and willingness to stand by it is often seen as indicative of courage, and therefore, true manliness. This trope is most prevalent in American works, where a "real man" is often also a "real American" (though exactly what entails a "real American" is often subject to the No True Scotsman fallacy), though it extends to all others who hold patriotism to their nation in high regard.
Hello, Unknown Troper. You'll need to get known to lend a hand here.