protective: +1 happy per military unit in a city
creative: each time city border expands, random great person is born(no
great generals are born this way)
nomad: stable enables mounted units to be spawned every few turns in
each city that has stable. Most powerful unit spawned is capped at light
cavalry (strength 8). Horses are still needed to build stable.
expansive: no pollution from population.
humanitarian: all pollution is cut in half