Previously, only whole units could withdraw from battle, but from this version, units can do so individually, so it is no longer necessary for all allies to withdraw in order to preserve a single allied unit that is about to die with lots of experience.
When you select "Withdrawal" in battle, a checklist of units will be lined up, and you must uncheck the units you wish to disengage.
When the "Decide Member" button appears, press it and only the unchecked units will withdraw from the battlefield and return to their home countries.
If you wish to withdraw all units together, click the "Withdraw All" button.