What is the main conflict in The Old Gringo by Carlos Fuentes?

Bierce is the old gringo referred to in this novel's title. The story focuses on the relationships the character forms in Mexico with Harriet Winslow, a schoolteacher from Washington, DC, and with General Tomás Arroyo, leader of the revolutionary band that is on its way to meet up with Villa's army. The three form a triangle, exploring questions of love, respect, and sensuality in ways that highlight the differences between Mexican and American ways of thinking. A few years after the book was published, it was adapted into a motion picture starring Jane Fonda, Jimmy Smits, and Gregory Peck as the old gringo.