What made the narrator kill his wife in "The Black Cat?"

The narrator
of seems to blame the root of all his problems in "" on alcohol despite the fact that
alcohol doesn't make most people suddenly abuse their loved ones. This inconsistency aside, it's
drunkenness that the narrator says makes him abuse his animals until one day the abuse goes so
far that he gouges out his cat's eye and kills it.

Soon after, another black
cat appears who also, strangely, is missing an eye, and he adopts it to replace the one that he
murdered. It's this cat who the narrator is too afraid to abuse (and who torments him) that he
blames for his increasingly abusive behavior toward his wife. One day he tries to kill the cat
(again?), but his wife defends it, and he kills her instead.