[Edi]

If you want a tougher AI for single player games, try the Better Independents mod. Once you learn to deal with the AI, you will soon get tired of every AI nation having the same horde of independents and the BI mod forces the AI to use national troops due to ´cost issues.

Just be real careful with the enslave mind and charm spells if you use the gold version of BI or you'll go bankrupt in no time flat.