Like all the novels Darling works on several different levels. First, it is a good story . . . kept moving, good characters, suspense, enough moving back and forth in time to tantalize you, but not so much as to totally confuse you. So, it is simply a good read.
It also worked as a "coming of age" story-although, read as just that, it would of course be a little over the top. Nonetheless, she goes through all the "typical" stages of adolescent rebellion (Weather Underground), forbidden love, independence from parents (how much more independent can you be than moving to Africa and never speaking to them!), marriage, child rearing, divorce/distance in marriage, empty nest syndrome, and replacement of familial ties with other objects of passion (here the chimps), death of parent, an attempt recapture "youth" (her trip back to Africa), and a second life post-retirement. During each phase she clearly develops a new personality (or at least changes in significant ways).
It also reads as a commentary on U.S. Foreign policy-which is what I think is implied in the title. Here she is, having gone through all of these "phases" in her personal life-joining a revolutionary underground which actually blows things up, fomenting revolution and mass slaughter in an African country, and living as a fugitive for decades. However, while the lives of everyone in Liberia are completely upended and made a living hell because of that country's revolution(s), her life ends up being virtually unaffected-she ends up as a "gentleman" farmer, about as normal an occupation as there is in the world, and all of her revolutionary activities, at least in this country, have, in the end, changed nothing-except her. Hence, she is, at the end, nothing but an "American Darling".
This is a fine allegory for the way the U.S. stumbles around the world, intervening in other countries, sometimes (but not usually) with the best of intentions, makes a holly mess, and then blithely disappears, blaming the country we've so thoroughly screwed up for being "backward" and beyond hope. Iraq anyone?