Is there any way to make Rome one faction?

[Atilius]

Hannibal99,

I you don't want to retain the Senate, simply do the stuff in the first section of this tutorial; it's the one Seasoned Alcoholic mentioned above. Then you should simply be able to remove the two remaining Roman factions and transfer ownership of their settlements to the Roman faction you wish to retain.

I think retaining the Senate with just one other Roman faction is possible, but it will get a bit strange because only characters of one faction can hold Senate offices. If you have trouble, reply and I will try to help out as time permits.