▁some ▁facilities ▁such ▁as ▁rec y cling ▁plants ▁and ▁nuclear ▁react ors ▁will ▁reduce ▁the ▁production ▁of ▁poll ution . ▁Additionally , ▁certain ▁events ▁such ▁as ▁space ▁launch es ▁and ▁use ▁of ▁nuclear ▁weapons ▁will ▁result ▁in ▁one - time ▁add itions ▁of ▁poll ution ▁each ▁time ▁that ▁they ▁occur . ▁ ▁An ▁initial ▁setup ▁feature ▁is ▁game ▁play ▁without ▁poll ution ▁problems . ▁ ▁H app iness ▁ ▁While ▁playing ▁the ▁game , ▁the ▁happiness ▁level ▁of ▁the ▁citizens ▁must ▁be ▁maintained . ▁If ▁a ▁city ▁is ▁far ▁away ▁from ▁the ▁capital , ▁is ▁over c row ded , ▁poll uted , ▁over work ed , ▁star ved ▁or ▁under pa id , ▁the ▁happiness ▁level ▁will ▁drop ▁with ▁ri ots ▁and ▁revol ts ▁occurr ing . ▁C ities ▁also ▁experience ▁unh app iness ▁during ▁w art ime , ▁especially ▁if ▁they ▁have ▁just ▁been ▁conquer ed ▁by ▁another ▁emp ire . ▁Many ▁terror ist ▁units ▁can ▁decrease ▁the ▁happiness ▁of ▁an ▁enemy ▁city . ▁For ▁example , ▁if ▁a ▁city ▁is ▁" in fect ed ", ▁it ▁will ▁lose ▁both ▁population ▁and ▁happiness . ▁If ▁the ▁happiness ' ▁level ▁goes ▁under ▁ 7 5 , ▁then ▁the ▁city ▁is ▁in ▁danger ▁of ▁ri oting . ▁If ▁a ▁city ▁ri ots , ▁it ▁does ▁not ▁produce ▁any ▁work ▁during ▁that ▁turn . ▁If ▁happiness ▁in ▁cities ▁continues ▁to ▁decl ine , ▁revolution ▁becomes ▁a ▁possibility . ▁If ▁that ▁happens , ▁the ▁city ' s ▁inhabitants ▁become ▁" bar b ari ans ",