They stopped farming and growing crops on one location and started growing and farming crops at another location. This enabled the soil to recuperate and gain the required minerals which makes good soil also fertile
Sparta was at controlling helots, by murdering them, terrorizing them, brainwashing them and beating them into submission. When the Spartans dominance eroded and Greece fell to Rome, helots still did not get their freedom. Instead Of being slaves in Sparta, they became slaves in Rome
Firsthand accounts : eyewitness account, letter from a general to his troops, an interview of a war veteran
Secondhand accounts: television documentary, article
In world war 2 computers were invented to help with aircrafts and other things. They were about the size of a whole room and now are very much faster and smaller.
