How can I split an army in Rome 2 Total War?

Only way to "split" an army seems to be having two generals. When you order a general to march to another general, you get a possibility to change troops from on army to another.

Compared to other TW games this seems like a huge drawback to be, because you dont seem to be able to recruit troops to undefended city if there is no general present nor can you leave troops to defend a city when your army marches on. City garrisons are usually not enough to defend a city and you need to carefully place your armies.

It does have a certain point, because roman armies were strictly hierarchical and there had to be a general leading it. It leads some inconsistencies tho, like in case your general is killed, you will be able to recruit a new one to that spot immediately.

You can exchange units between 2 generals at least. But as far as I know, all units must be in the company of a general or an admiral (except for agents ofc)

Also, the number of generals you can have at any given time is dependant on your "imperium". You recruit generals from city centers.