This is called a western action book. I am not a western fan but did enjoy this book. I found that the western action takes place as the lawless days of the old west were nearly over. The story really takes place in Mexico which is befitting to this charismatic tough guy.
The story is really about a well off guy from a rich family that simply cannot stand the boring life of banking in Hong Kong. He gets the opportunity to try a stint as a mercenary and his life is changed forever. The book is about his escapades during various periods of unrest and a failed attempt to take the northern Baja Mexico area and secede from the government in Mexico City.
The story does slow down at times but is generally fast paced, As you read the book, see if you can pick out the secondary character that becomes the center of a subplot. A pretty good yarn.