Answer:
It means that Vietnam, with its different culture and language, its different ideals, and particularly, with its perseverant soldiers and really difficult terrain, became a true test to an American´s deep-felt belief in the protection of freedom and democracy, and the rule of the people, especially when they saw the war would not be fought, or won, in any easy way, and that the Vietnamese were ready also to die for their own beliefs.
Step-by-step explanation:
Joseph Eugene Sintoni was an American soldier from Massachussetts, who died on March 27, 1968, after having fought in the Vietnam War. In a letter written to his fiancee in case of his death, he tells her, among other things, about the truths of Vietnam, and especially, how little Americans know about it, thinking it just a remote place in the world. In a very short sentence, this man simply tells Angela, his fiancee, that Vietnam has been a true test of the American spirit, and later he explains a bit about it. The desire of Americans for freedom, their constant fight to uphold that one unalienable right, and insipre it in other nations. That is how he also justifies his own role in Vietnam to her; as his duty as an American to help his country to excert its God-given task in the world, of defending freedom and democracy.