Yes, I was surprised too.
Looked through the code:
Consts.py:
Code:
lNewWorld = [rAustralia, rOceania, rCanada, rAlaska, rUnitedStates, rCaribbean, rMesoamerica, rBrazil, rArgentina, rPeru, rColombia]
UniquePowers.py:
Code:
...
# get available migration and immigration cities
lSourceCities = []
lTargetCities = []
for iPlayer in range(iNumPlayers):
if iPlayer in lCivBioNewWorld and not utils.isReborn(iPlayer): continue # no immigration to natives
pPlayer = gc.getPlayer(iPlayer)
lCities = []
bNewWorld = pPlayer.getCapitalCity().getRegionID() in lNewWorld
for city in utils.getCityList(iPlayer):
iFoodDifference = city.foodDifference(False)
iHappinessDifference = city.happyLevel() - city.unhappyLevel(0)
if city.getRegionID() in lNewWorld and bNewWorld:
if iFoodDifference <= 0 or iHappinessDifference <= 0: continue
iNorthAmericaBonus = 0
if city.getRegionID() in [rCanada, rUnitedStates]: iNorthAmericaBonus = 5
lCities.append((city, iHappinessDifference + iFoodDifference / 2 + city.getPopulation() / 2 + iNorthAmericaBonus))
elif city.getRegionID() not in lNewWorld and not bNewWorld:
iValue = 0
if iFoodDifference < 0:
iValue -= iFoodDifference / 2
if iHappinessDifference < 0:
iValue -= iHappinessDifference
if iValue > 0:
lCities.append((city, iValue))
if lCities:
lCities.sort(key=itemgetter(1), reverse=True)
if bNewWorld:
lTargetCities.append(lCities[0])
else:
lSourceCities.append(lCities[0])
...
In ordinary game there are no civs that have capital in Australia/Oceania, so immigration mechanic affect only America, Canada and, to a lesser degree (due to modifier for NA civs), Mexico, Argentina, Peru, Colombia and Brazil.
But if you are playing as Polynesia, still playing after 1772 year, and acquired enough happiness to overcome USA +5 modifier, you can get immigration moments too.
Why not? Dealing with instability is pain (I can deal with overextension from Australia and Philippines, I can deal with useful but outdated Republic civic, but not both), but it is still unusual and interesting game.
(Though, it is hard not to win URV)