Nicholas Ostler's Empires of the Word is wide ranging examination of how languages evolve, spread, and die out.
Ostler takes a wide view: we move from India, to China, to Arabic speaking countries, to Europe and end on English, the current lingua franca.
Ostler’s book is fascinating, and VERY detailed, so it demands some patience on the part of readers. But readers will be rewarded for their effort with some firm analysis of the complexities of how languages live and die.
Ostler does not leave us with any hard and fast rule about why some languages spread and others do not. Often, language spread because of conquest, as Latin did; or through a combination of conquest (British English) and prestige (American English).
Language is as complex and as multivariate as we are; really, we should expect no less.