trade creation and diversion
Suppose three bakeries supply your town: a cheap one across the river that you must pay a bridge toll to reach, a slightly pricier one in the next county, and an expensive one downtown. Now your town strikes a deal that waives the toll for the next-county bakery only. Two things can happen. You might switch from the dear downtown baker to the now-attractive next-county one — a good change, you pay less. Or you might switch away from the genuinely cheapest cross-river baker, who is still tolled, to the next-county one — a wasteful change, because the cheapest source got shut out by the toll. These are trade creation and trade diversion.
When countries form a free-trade area or customs union, they drop tariffs among members but keep them on outsiders. Trade creation happens when this lets a member buy from a lower-cost partner instead of producing the good expensively at home — new, efficient trade is created, and the union gains. Trade diversion happens when the tariff-free deal makes a member buy from a partner that is not really the cheapest producer, simply because outsiders still face tariffs — trade is diverted away from the truly lowest-cost world supplier to a less efficient member, which is wasteful. The Canadian economist Jacob Viner introduced this distinction in 1950, and it overturned the easy assumption that any move toward free trade must be good.
The crucial lesson is that a preferential trade bloc is not automatically beneficial — its value depends on whether trade creation outweighs trade diversion. A union that mostly diverts trade to high-cost insiders can actually leave the world, and even its own members, worse off than before, because cheaper outside suppliers are locked out by the common external tariff. This is why economists distinguish such regional deals from true global free trade: lowering barriers for everyone always creates trade, but lowering them for a chosen few can divert it. Measuring which effect dominates in any real agreement is genuinely difficult and often contested.
Two neighbouring countries form a customs union and drop tariffs on each other's cars. If they now buy efficient cars from each other instead of making poor ones at home, that is trade creation. But if they switch from importing cheaper, better cars from a third country (still tariffed) to each other's pricier ones, that is trade diversion — and the union may have made them worse off.
A trade bloc helps only if the trade it creates outweighs the trade it diverts.
A regional trade deal is not always good. If it mostly diverts trade to higher-cost insiders rather than creating new efficient trade, it can leave members worse off than open global trade would.