Slitherine

"Your orders are to occupy your objectives and encircle them. Once surrounded, they will have little choice but to join us."

I completely surrounded 4 Romanian units, but they did not surrender and attacked instead. I had left 2 objectives vacant for the Romanians to capture once they had changed sides. 2 Romanian surrounded units (1 infantry, 1 tank) are occupying objectives under Romanian ownership. So what am I not doing right?

IIRC the Romanians switch sides once you take all of the initial objectives. Don't worry about leaving some objectives for the Romanians to capture--they will have their hands full as soon as they switch sides.

Does all of the 'all of the initial objectives' mean all of the highlighted ones except for the 2 highlighted ones occupied and owned by Romanian troops? If so where do the extra objectives come from, or does one receive additional objectives one the Romanians change sides. Also there is a third highlighted objective in the south east owned by Germany occupied by Romanian mountaineers. What does one do about that one?

To be honest the orders are as clear as mud. RL Battles have been lost because of muddled orders.

You force the Romanians to change sides by capturing the initial set of marked objectives.
If they change sides they get some new objectives.

I would have preferred the bit about what happens after changing sides in an in-game message, as I tried surrounding individual units in my first time round.

Thanks amigo. That makes things clearer. What about the highlighted objective in the south east owned by Germany occupied by Romanian mountaineers? I guess you have to kill or dislodge?

It's only the gold-rimmed victory hexes that matter, but you do have to capture all of them. That should force the Romanians to change sides.

I don't think I'm giving away too much, to note that it's mentioned in the briefings that the Romanians have to do some work after you capture all the initial victory hexes, so you will need a few turns in hand, though I think you get MV for getting them to change sides even without the extra missions.