If free trade will benefit all nations in the long run, why do nations so often establish barriers, like tariffs, to make free trade impossible?

the reason nations in the long run why do nations so often establish barriers, like tariffs is: nations often seek to protect their firms and their workers from competition by imposing barriers like tariff, a nation will increase the selling price of that product in the market, which make it easier for local business that produce similar product able to compete and nations often seek to protect their firms and their workers from competition. free trade implies that nations can import and fare products with no levy hindrances or other non-tax boundaries to exchange. basically, unhindered commerce empowers bring down costs for buyers, expanded fares, profits by economies of scale and a more prominent selection of merchandise.nations  so often establish barriers, like tariffs, to make free trade impossible because "nations often seek to protect their firms and their workers from competition," since free trade can lead to a great reduction in gdp sometimes. 

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