Trade Routes in the Late Roman Empire
I mean, any idiot can write bad alternate history. Very simple, just change an inconvenient fact or three and wham, alternate history.
What is mind-bleedingly difficult is figuring out the implications of your one or two facts a few centuries down the road. You need to be a sociologist, economist, and a couple other -ists.
Which leads me to a book called Charlemagne, Mohammed, and the Making of Europe. It's a look at the Pirienne Hypothesis in the light of archaeological evidence, primarily pothserds and numismatics. P was a Belgian historian who hypothesized that the Germanic invaders of the Western half of the Roman Empire really didn't change a great deal when it came to societal and commercial patterns, and that only the severe dislocations caused in the Eastern Med by Islam sufficed to bring about the Carolingian world a century and a half later.
Not so much so, but in the interests of exploring what did happen, some interesting things are brought to light. This book is hard to summarize, but it manages to show the outlines of trade routes which stretched from China and Burma all the way to England and explains why Chinese silk is found in a Viking's grave in Sweden. Also explains why the upswing of Viking raids happened in the 820-830 time frame. There was civil war in the Caliphate, and that disrupted global trade patterns, impoverishing folks who got used to making quite a profit. Of note is the fact that the actual money (Arabic dinars) was of little value to the Norse except as decoration, but of great value to the Franks who melted it down and minted the denir, the French penny, in almost exactally the same size and weight.
Post-Roman Western Europe has never been one of my main interests, as it generally is too depressing to get into heavily (smelly barbarians running about hitting each other with axes, mostly), but this is good stuff.