I have made multiple attempts to beat the Single Player map Race to the Middle. Each time has resulted in failure. I attempted to rush to the middle with large armies and got wiped out. I tried to circumvent the middle by sneaking into other castles to try to take them out, only for the enemy to take me out.

This stems from the AI at the West Castle having a headstart towards the middle. By the time my approach begins, it has already claimed the middle and thus renders any attempts to stop it moot.

Attempting to replicate strategies I have seen on the forum have resulted in failure. Requesting assistance in beating map, as I am losing my mind...

Don't bother with Fissel, he's a troll.

My best advice for dealing with the AI is to break its bonuses, and keep them broken, while protecting your own bonuses from being broken. But definitely break its bonuses. That's the key.

Just rush to the middle. The moment you reach it there shouldn't be an Ai in control of the entire middle (although the Ai from the west might have both middle territories that you can see)