Often the question arises what is the role of the neutral countries in the game and how can I use them to benefit from. In the majorities of games they are not useful but from time to time they are of strategic use.
Spain (SPA): At the time the allies land in Spain the pressure on WEU can increase tremendously from one minute to the other. Therefore it is very important that Germany has stationed enough tanks in GER, which can, in collaboration with infantry from WEU and air units, react to the landing of the allies in SPA.
Mongolia (MNG): Useful for Japan in order to put pressure on NOV. Either you have all units in MNG or divided in a way that one half is in SIN or YAK and the other half in MNG. If the allies attack one of the two halves the other would instantly be able to hit NOV or the just attached country. Furthermore the allies have to be careful if YAK is under allies? control but Japanese tanks are stationed in MAN. If Germany liberates MNG during his turn then the Japanese tanks in MAN are now in range of NOV. The same tactic also works reversed: If Russia has enough tanks in NOV to attack MAN, then USA can liberate MNG. Certainly it has to be evaluated in front if the sacrifice of Russian tanks for the Japanese units is a pay-off.
Turkey (TUR): Especially of interest for England. By placing arm and inf in TUR pressure is put on SYR and EGY. The advantage in comparison against PER is clear: Japan cannot hit the units by an attack from RED. TUR might be advantageous for GER in the first round if at least the tanks are still present in UKR. In this case TUR will be either taken using the transporter or taken by flying over. After capturing CAU the tanks are moved to TUR in the non-combat phase and threatening from that point Africa, PER and IND.
Columbia (COL): Columbia is one of the countries Japan might take if it is planning to attack Brazil. In case that e.g. in MEX or WUS units are stationed, who would be able to attack Panama you can attack BRA anyway via COL in the following round. A similar situation is if allied ships are in range of CAR preventing an amphibious attack by a transporter, BRA can be attacked via COL. Although in this situation you should be very careful because trn in CAR can also attack COL. If a Japanese invasion of BRA is possible US can react by moving one inf to PAN. With this inf the US can take COL in the following round while moving tanks from WUS to PAN. These tanks can then attack BRA in the following round. Of course Japan can prevent US from moving tanks to PAN by strategic maneuvers (e.g. moving transporters to EPO).
Switzerland (SWZ): Switzerland may become important, when you decide to invade Germany by using transporters. UK passes Switzerland with an air unit before attacking Germany. Therefore US-bombers, which have been produced the last turn and now standing in WUS or EUS can now participate in the attack. US-fighters starting from MOS, ALG, LIB, CAU and GBR can now participate, too although no carrier is available in BAL. If GER or JAP conquers Switzerland to prevent the previous described scenario then Switzerland can also be used as a retreat country for an additional AA-gun, when SEU/WEU/EEU has to be evacuated.
Afghanistan (AFG): It is maybe useful as a retreat option for units that are coming from a deadzone. The advantage of AFG is that it is still threatening a lot of other countries. An example would be British units in IND, which are threatened by the Japanese fleet in a way that they should not be stationed at the shore or in SIN.
Argentina (ARG): Taking ARG makes only sense if you are planning to capture BRA, but enemy air units are placed in a way that they would be able to attack the units and the transporters together. By landing the units in ARG directly you can at least prevent the risk to loose the troops and ships in one attack. Because of ARG has 3 coasts you will most likely find a sea zone, which is not in range of the enemy air units.
Bolivia (BOL): Same as ARG, but BOL has only one coast (sharing with ARG) and is therefore not of interest.
Sweden (SWE): Sweden is taken scarcely by Germany in turn 1 in order to rescue the FIN-units. But it is very difficult to use these units effectively in the later game because you would need air support and the German air fleet usually has others more important things to do. SWE may become important for the allies if Ger is in possession of LEN. Attacks on FIN are much safer, because you can prevent an amphibious attack. Moreover you can occupy FIN with much more units if you already have units stationed in SWE.
Saudi-Arabia (SAR): In special occasions useful as additional landing zone for allied fighters, which are attacking RED. Japan is maybe forced to keep distance to RED. Maybe also interesting for Japan as a retreat option for units from Africa if the pressure on PER is too high. But in general this country is not recommended.
Rio de Oro (RIO): Retreat country for allied inf, either after a disastrous Africa-attack or after a Japanese attack in EGY without the chance of an allied counter-attack.
Angola (ANG): ANG is a good base in order to transform KEN/SAF into an exchange country.
Mozambique (MOZ): Exactly reversed than ANG. If the Allies are strong in EGY then Japan can use MOZ as a base to attack SAF and KEN.
Irland (IRE): Total nonsense. It might be imaginable that a US-rocket can be placed there if the rocket cannot be placed in FIN or Africa.