For those who haven't played Italy, you have a regional decision card and if this is played steadily on the Italian minors will mean that come 1865 Italy south of the Po unifies. Its clear from reports that Sardinia-Piedmont (S-P) is only doing this consistently in Rome, meaning the other minors (Parma, Tuscany and the Two Sicilies) stay independent. The key issue here is that decision that rounds up all these sub-steps relies on all to have happened as:
SelectFaction = $ITA
SelectRegion = $Lazzio
StartEvent = evt_nam_PIE_ItalianUnity1870|1|2|evt_txt_ITA_RomeCapital1867|Event-img_ITA_RomeCapital1867|$Lazzio|NULL
MinDate = 1866/01/01
MaxDate = 1875/03/10
Probability = 50
EvalEvent = evt_nam_ITA_Unification1871;=;0
EvalEvent = evt_nam_ITA_Parma_UnificationOK;=;1
EvalEvent = evt_nam_ITA_Toscana_UnificationOK;=;1
EvalEvent = evt_nam_ITA_PapalStates_UnificationOK;=;1
EvalEvent = evt_nam_ITA_TwoSicilies_UnificationOK;=;1
So these events are designed to make it likely that the chain will end up working as intended.
There are some assumptions I've made.
The AI must somehow take in Rome - from all reports it tends to do this. My logic is that there was a small trend in Piedmontese politics that rejected unification with the south and saw a future for S-P as a 'Sparta of the nineteenth century' with a small well trained army and a powerful industrial base. So this allows the very unlikely, but possible, outcome that S-P turns its back on unification post-Cavour.
Should stress that here I am only interested in revising this chain up to 1870 - so this is not an attempt to model a non-unification decision into a later iteration.
If Rome is S-P held, then a set of agitations will occur in Parma and Tuscany that will, almost certainly, bring them into the new state.
If Rome is S-P held, this will set off tensions with the Two Sicilies. This tension will either end in unification (as set up by the alternative chain) or a full war between the two states. Full War is important as it will force the campaign to a conclusion - one or the other will end up ruling all of Italy, there is no lesser peace available (this of course models the American Civil War).
I think S-P will win, but it will then be hampered by unrest etc.