Hills Causation Criteria outlines the minimum requirements required to construct a causal relationship between two components. These conditions were initially proposed by a British medical statistician named Austin Bradford Hill (1897-1991), as a way of identifying the causal link between a particular attribute (e.g. cigarette smoking) and a disease ( e.g. lung cancer). Although it is quite easy to say that agent for example smoking causes disease such as lung cancer, but on the other hand it is quite contrary to create a clear, statistically relevant relationship between the two cases.
People didn't have money so they trade for things they wanted or if they didn't want it they will still take it and trade it to someone that did want it
