Short answers, pulled from the story.
Protectionism is an economic policy that uses tariffs, import quotas, administrative barriers, anti-dumping legislation, direct subsidies, export subsidies, and exchange rate control to restrict imports. These measures aim to protect domestic producers and wage rates from lower-priced foreign competitors.
Economists state that protectionism creates deadweight loss which benefits no one unlike free markets where such total loss does not exist. A 2016 study found trade typically favors the poor as they spend a greater share of their earnings on goods while free trade reduces costs for consumers.
Europe became increasingly protectionist during the eighteenth century but countries like the Netherlands Denmark Portugal and Switzerland moved toward free trade prior to 1860. The repeal of the Corn Laws in 1846 marked a decisive shift toward free trade in Britain followed by treaties signed with Belgium in 1861 and Italy in 1863.
From 1790 to 1860 revenue considerations dominated import duties accounting for approximately 90% of federal government receipts before shifting focus to protecting domestic industries from 1861 to 1933. From 1934 to 2016 the primary objective became negotiating trade agreements after the Great Depression led to political realignment following the Democratic victory in the 1932 election.
Protectionism has been attributed as a major cause of war with proponents pointing to constant warfare in the seventeenth and eighteenth centuries among European countries whose governments were predominantly mercantilist. Archaeologist Lawrence H. Keeley argues disputes between trading partners escalate to war more frequently than disputes between nations that do not trade much with each other.
Heads of the G20 meeting in London on the 2nd of April 2009 pledged they would not repeat historic mistakes of protectionism yet 17 of these 20 countries imposed trade restrictive measures since then. Economists estimated new measures taken through late 2009 distorted global merchandise trade by 0.25% to 0.5% while President Donald Trump announced in January 2017 the U.S. was abandoning the TPP deal.