The Fall of the Roman Empire, by Peter Heather

If you're looking for a thorough, basic book on the fall of Rome from a modern perspective, Peter Heather's The Fall of the Roman Empire would be a good choice. It has its own agenda, but so do the Christianity-focused (Gibbon) and economic-focused (AHM Jones) classic works on the fall of Rome.

The opening scene in 54 B.C. shows a Roman legion emerging from its winter camp only to be ambushed by the Germanic-speaking Eburones. The second chapter begins with the Teutoberg Wald disaster, followed by the butchery of the Sasanian Dynasty which flayed the Roman emperors Numerianus and Valerian. These dramatic moments are not just pivotal events in Heather's history of the fall of Rome, but demonstrate Heather's view of history -- that understanding history is like (reading) a detective story. The reader is enjoined to become part of the jury to decide whether Heather has proven his case.

Heather makes points that need to be taken as Roman history mantras. Among these are that the Roman Empire endured for a very long time, and even if Gibbon's 476 date is taken as the end, rather than the fall of Constantinople or the rise of Islam, the Roman Empire lasted half a millennium, and that no serious historian should believe that the western Empire of Rome fell entirely because of internal problems, or exogenous shock (p.445).

Heather's thesis is that the various assaults on Rome had ripple effects. Rome lost territory and revenue, was spread too thin militarily, and the barbarians on the border kept growing stronger. One attack was not enough, but the cumulative effect caused the fall of the western empire.

Read The Fall of the Roman Empire to get the details.