The simplest rule for Italy would be:
In Spring 1915 Italy must decide.
If, at the end of Winter 1914/15, The CPs control a mainland tt of France, then Italy joins the war on the side of the Central Powers.
If France is still free of occupation, then the Allies can pay X IPC (to the bank!) to persuade Italy to join the war on their side.
If neither condition is met, then Italy declares neutrality for the duration, and can only be activated if somebody attacks it.
Suggestions for some other countries:
Serbia is assumed to begin at war due to the declaration of war and being shelled by Austria in July. Same for Montenegro?
Turkey joins the CP immediately any CP warship docks in the Sublime Porte. It will not join the Allies as long as Russia is a member.
http://en.wikipedia.org/wiki/Pursuit_of_Goeben_and_Breslau
Bulgaria will join the CP when Serbia is invaded by a CP army of at least 6 units. Bulgaria is immediately activated and may join in the attack on Serbia.
Possibly allow the Allies to pay cash to keep Bulgaria out?
http://en.wikipedia.org/wiki/Bulgaria_in_WWI#The_end_of_neutrality
Portugal - depends on the map including southern Africa; Portugal’s main reason for hostility to Germany seems to have been German designs on Angola:
http://en.wikipedia.org/wiki/Portugal_in_World_War_I
Romania has a choice, since the CP (Bessarabia) & the Allies (Transylvania) can both offer it a majority Romanian province from a defeated enemy. Romania demanded military back-up, so perhaps something like:
Romania will join the Allies if at least 6 Allied land units invade Transylvania. Romania can join in this attack.
Romania will join the CP if at least 6 CP land units attack Bessarabia. Romania can join in this attack.
Gives a rather nice dynamic to the Austria-Russian conflict.
http://en.wikipedia.org/wiki/Romania_during_World_War_I
USA. Reading the rules for Paths of Glory:
http://www.gmtgames.com/living_rules/pog_rules_2004.pdf
the game has a built-in mechanism whereby American entry is accelerated by Russia’s decline, the two events calculated to balance.
The simplest way is:
If/when Russia is reduced to “disorder” status (q.v.), then Germany (if it has not already done so) automatically declares unrestricted sinking of Allied ships.
The idea here is that, with Russia in chaos, Germany believed it could finish off the western powers with men freed from the eastern front before America could get mobilized; therefore America declares war the turn after Russia falls into disorder (i.e. the fall of the Tzar/February Revolution). Remember that America had a very small standing army so it’ll take time for the Yanks to arrive in numbers. This is what Germany has to calculate when pushing hard against Russia; it still has to push Russia further before Revolution knocks it out of the war altogether.
Ideally, if Russia stays in the war there has to be a chance for the Allies to win without American support.
Greece evidently had difficulty with its German king. In effect, the country could be said to have joined the Allies in 1915 when they invited in Allied forces (Salonika) in response to Bulgarian entry into the war.
But since this was opposed by the King, war was not officially declared until he left the country in June 1917.
So…
If Bulgaria enters the war on the CP side; Allied forces may occupy any Greek tt other than Athens (i.e. Crete, Salonika, Corfu).
Greek forces may help defend these tts, but may not attack others.
If the CP attacks any Greek tt to fight Allies based there Greece is moved to “at war” status.
http://en.wikipedia.org/wiki/History_of_Modern_Greece#World_War_I
I shall also post:
1. Much simplified version of the above
2. Suggestions for countries that remained neutral (Netherlands, Spain, Scandinavia)