Yes, I was the source of all your problems from about turn ~40 onwards.
I would have attacked you directly, but I was hoping to use Plague + Raven Feast + Lichcraft to convert all my enemy's population into death gems and liches. Unfortunately, it takes a full month for the plague to take effect, so the unburied corpses in a province are reduced before you can cast the Raved Feast on the province and collect your gems. This means that rather than getting a net ~15 gems per casting, you only get a net ~4 or so. So much for my geometrically growing army of liches.