It is now possible to block diplomacy towards some countries, e.g. the USSR cannot attempt to influence Franco's Spain. We have also introduced the ability to limit investment towards historically neutral countries, so that, for example, only a small diplomatic effort can be made to swing Switzerland towards one side or the other.
Nice, historically only the UK and US applied diplomatic pressure; via threatened and actual embargoes, to keep Spain neutral. This change increases, slightly, the chance that Spain can be influenced to join the Axis. Will the SC3 AI ever launch a diplomatic campaign to sway Spain to its side given that it takes a sizable investment; at least it did in SC2, to have a chance of this succeeding.
Yes there will be games where the Axis will have successfully caused Spain to join its side.