The "ugly American" symbolized the attitude of Americans who displayed their arrogance when working or living in other countries. These Americans didn't understand or respect the local culture of the people and didn't address the real needs of the people. The book was written to point out the failure of the U.S. to defeat Communism in Southeast Asia during the Cold War between America and the Soviet Union.
All of the character are used to reflect what was right or what was wrong with the U.S. strategy of stopping Communism in these countries. The American characters are shown to either be a part of the problem or a part of the solution. Ambassador Sears characterizes the American who knows nothing about the country to which he's assigned and makes no attempt to find out. Joe Bing represents those who considered the locals to be inferior and that it was better for the locals to have to learn to speak English. Major Wolchek realizes that the American way of fighting has to be changed to guerilla warfare, but the French and Americans ridicule him. On the other side, Father Finian and Colonel Hillandale show how important it is to understand and respect the local culture.
The Russian characters are very different than the Americans, however. They go into the villages and learn to speak the language and understand the culture. They understand this is necessary in order to spread propaganda in these countries and get the local people to trust Communism. They are well-trained in their missions.
Each story is a parable that shows the foolishness of U.S. policy or depicts that there was a positive alternative that could have been put into place. The message is told in black-and-white. There aren't any subtleties about what is being said. The characters are used to tell the story in this fashion. Several of the characters do have opposites in order to underscore the message throughout. The U.S. did not meet the needs of the local people, and the diplomats were ineffective in winning the local people to their side.