In his excellent and accessible book The Fall of Rome And the End of Civilization, Bryan Ward-Perkins displays a table (3.1 – in German) with "A list of 210 reasons, from A-Z, that have been suggested, at one time or another, to explain the decline and fall of the Roman empire." It begins with Aberglaube (superstition) and ends with Zweifrontenkrieg (two-front war). As you can imagine, some of it is hilarious!
The list was compiled by Alexander Demandt, a German Professor of Ancient History at the Free University Berlin, in his book "Der Fall Roms: Die Auflösung des Römischen Reiches im Urteil der Nachwelt". Some of you may be familiar with him as editor of Theodor Mommsen's lecture transcriptions, A History of Rome Under the Emperors.
I did some googling and found an English translation:
Unfortunately, the German list seems not to be available online; it reads even funnier in the original, there is a lot of "Über...". In the translation, it begins with Abolition of gods and ends with Vulgarization. #203 is Tristesse . . .