The US is currently facing a government shutdown because Donald Trump is insisting any spending bill must fund the construction of a US-Mexico border wall, which would cost as much as $18 billion. In a paper published late last year in The Economic Journal, economists Evelina Gavrilova and Floris Zoutman and sociologist Takuma Kamada found that the creation of a domestic marijuana industry—in the form of legal markets for medical marijuana—led to a 12.5% reduction in violent crime in US states bordering Mexico. The researchers were testing a fairly simple hypothesis: Introducing legal marijuana markets decreases the revenue that drug-traffickers earn from smuggling illicit substances. In turn, that reduced revenue leads them to invest less in crime.  The creation of a domestic marijuana industry led to a 12.5% reduction in violent crime in states bordering Mexico. The authors used federal records to track crime rates over time as different states introduced laws to allow limited marijuana use, and found significant reductions in drug-related assaults, robberies and murders. The effects are concentrated in border states, where cartels engage in disputes over smuggling routes and territory. The best border wall is a legal marijuana market

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