This book is all about Andrew Pham, a Vietnamese young man who was raised in the United States (California, to be exact). Pham describes himself as one of the "boat people" from Vietnam at the beginning and, in fact, Pham's father was a Prisoner of War (on the Vietcong side). In the midst of dealing with his past (as well as the suicide of his sister which makes up his present), Pham decides to ditch the life he knows and ride his bike for a year.
The majority of the book is about Pham's bicycle journey hence the "Two-Wheeled Voyage" of the title. From his home in California, we ride with Pham as he traverses the desert in Mexico. Switching places and continents entirely, he then rides another thousand miles in a purposeful circle in Japan from the city of Narita to Kyoto. In a few more months (and almost three thousand miles), Pham is in Saigon where he is incredibly disheartened.
Here I find nothing familiar in the bombed-out darkness.
In his own, native country of Vietnam, the natives think he is either from Japan or Korea. (In America, of course, the anti-Vietnam Americans of the 70s never consider Pham truly a citizen.) Only his relatives know the truth.
In conclusion, realize that this is a true search for identity in the midst of a completely different culture for Pham. In short, Pham learns that humans are all subject to the "human condition," no matter what their culture.