A lot of people from both political sides seem to trash this book for some reason. Never understood why and can't find an explanation.
While you wait for answers, check out the FAQ section for previous responses about Guns, Germs, and Steel.
https://www.reddit.com/r/AskHistorians/wiki/historians_views#wiki_historians.27_views_of_edward_gibbon.27s_.22decline_and_fall_of_the_roman_empire.22#wiki_historians.27_views_of_edward_gibbon.27s_.22decline_and_fall_of_the_roman_empire.22