▁and ▁other ▁dis aster s ▁led ▁to ▁a ▁considerable ▁decl ine ▁of ▁population . ▁ ▁As ▁a ▁result ▁of ▁this ▁collapse , ▁free ▁resources ▁became ▁available , ▁per ▁cap ita ▁production ▁and ▁consumption ▁consider ably ▁increased , ▁the ▁population ▁growth ▁res umed ▁and ▁a ▁new ▁soci ode m ographic ▁cycle ▁started . ▁It ▁has ▁become ▁possible ▁to ▁model ▁these ▁dynamics ▁mathemat ically ▁in ▁a ▁rather ▁effective ▁way . ▁Note ▁that ▁the ▁modern ▁theories ▁of ▁political - dem ographic ▁cycles ▁do ▁not ▁den y ▁the ▁presence ▁of ▁tr end ▁dynamics ▁and ▁attempt ▁at ▁the ▁study ▁of ▁the ▁interaction ▁between ▁cy clic al ▁and ▁tr end ▁components ▁of ▁historical ▁dynamics . ▁ ▁Four th ▁Turn ing ▁theory ▁▁ ▁The ▁Stra uss – H owe ▁gener ational ▁theory , ▁also ▁known ▁as ▁the ▁Four th ▁Turn ing ▁theory ▁or ▁simply ▁the ▁Four th ▁Turn ing , ▁which ▁was ▁created ▁by ▁authors ▁William ▁Stra uss ▁and ▁Neil ▁How e , ▁describes ▁a ▁the or ized ▁rec urr ing ▁generation ▁cycle ▁in ▁American ▁history . ▁According ▁to ▁the ▁theory , ▁historical ▁events ▁are ▁associated ▁with ▁rec urr ing ▁gener ational ▁personas ▁( arch et ypes ). ▁Each ▁gener ational ▁persona ▁un le ash es ▁a ▁new ▁era ▁( called ▁a ▁turning ) ▁in ▁which ▁a ▁new ▁social , ▁political , ▁and ▁economic ▁climate ▁exists . ▁Turn ings ▁tend ▁to ▁last ▁around ▁ 2 0 – 2 2 ▁years . ▁They ▁are ▁part ▁of ▁a ▁larger ▁cy clic al ▁" sa ec ul um " ▁( a ▁long ▁human