links the emergence of the Sicilian Mafia to surging demand for oranges and lemons following the late 18th century discovery that citrus fruits cured scurvy. A 2016 study argues that petrostates may be emboldened to act more aggressively due to the inability of allied great powers to punish the petrostate. The great powers have strong incentives not to upset the relationship with its client petrostate ally for both strategic and economic reasons. A 2017 study found evidence of the resource curse in the American frontier period of the Western United States in the 19th century (the Wild West). The study found that "In places where mineral discoveries occurred before formal institutions were established, there were more homicides per capita historically and the effect has persisted to this day. Today, the share of homicides and assaults explained by the historical circumstances of mineral discoveries is comparable to the effect of education or income." A 2018 study in the Economic Journal found that "oil price shocks are seen to promote coups in onshore-intensive oil countries, while preventing them in offshore-intensive oil countries." The study argues that states which have onshore oil wealth tend to build up their military to protect the oil, whereas states do not do that for offshore oil wealth. A 2020 study determined that low levels of oil and gas revenue actually increases the likelihood of nonviolent resistance in autocratic countries, despite the general logic of the resource curse. Democracy and human rights Research shows that oil wealth lowers levels of democracy and strengthens autocratic rule. This is because political leaders in oil rich countries refuse democratic development because they will have more to give up from losing power. Similarly political leaders of oil rich countries refuse democratic development because political elite collect the revenues from the oil export and use the money for cementing their political, economic and social power by controlling government and its bureaucracy Military spending generally increases with oil wealth, meaning that a military coup - one of the strongest tools in toppling autocracies - is less likely in oil rich countries given that dictators can quell resistance through additional funding. According to Michael Ross, "only one type of resource has been consistently correlated with less democracy and worse institutions: petroleum, which is the key variable in the vast majority of the studies that identify some type of curse." A 2014 meta-analysis confirms the negative