Currently the Mauryas and Persians have a 10% population cap bonus (i.e. 330 instead of 300), while the Spartans have a 10% penalty (i.e. 270 instead of 300). The rationale behind it seems to be that the former two were vast empires and therefore had large populations (and armies), whereas the latter was merely a city-state. However, this is an accident of history: the size of populations has nothing to do with anything specific to the civilizations: a large area can simply support a large population: had the Mauryas lived in the Peloponnese, they would have had only a small population, and had the Spartans lived in India, they might have conquered a vast area.
Scenarios can set their own population caps for players, but in random maps (and skirmishes), the players' factions shouldn't influence their population cap: all are supposed to have equivalent positions and equal chances to win. Having these civ-specific population bonuses flatly contradicts 0 A.D.'s “what if ...” premise.
This patch therefore removes those flawed population cap civ bonuses.