How to fight 70-100k HRE army?

[Gooner]

The HRE was created very early in my game (around 800s). It's now 1100s, so it's been very stable for about 300 years. It has never even come close to breaking up. Any rebel that pops up has only like 10-20k men, against their mega army. I have Sicily and most of Southern Italy. I can't go further north without engaging the HRE, but they have 70-100k men. I have 20-30k men depending on my relationships with my vassal and my own martial ability. How do I even go about winning against such overwhelming odds? I tried parking my army (my own levy + my retinue + my vassal's levy) on a mountain and it still got crushed by getting outnumbered by over 20k.

 

[WomboCombo]

Join them and subvert them from the inside.

 

[Seclouds]

Join in the demon worship, be the high priest and recruit their hire, they will agree anything you ask.

 

[DPS]

Either save up money for lots of mercenaries, or expand in other directions until you can take them on with more even odds. Or build up enough grace with China to get China to shatter them for you if you have Jade Dragon and are within diplomatic range of China.

 

[Kumicho]

You're playing as Sicily, go have fun beating up on the Muslims! CO conquer your way east or west, taking out anybody in Hispania (if you started in the 769 date it's probably still all Muslim), or go east and start beating up on Egypt and the holy lands! Conquer a bunch of territory and you'll be in a far better shape to take him on.
Or just marry your way in to an alliance with the ERE, but remember that if they have another war (revolt, etc) they'll abandon your war to go fight their own.

 

[ScienceNerd]

Swear fealty and eat their vassals.

 

[Narvait]

Join them, eat them from inside.
Or the good old ‘marry and kill the spouse’s family’ game.
Or just assassin Emperors one by one until the whole thing breaks into chaos.