New trade theory (NTT) is a collection of economic models in international trade which focuses on the role of increasing returns to scale and network effects, which were developed in the late 1970s and early 1980s.
New trade theorists relaxed the assumption of constant returns to scale, and some argue that using protectionist measures to build up a huge industrial base in certain industries will then allow those sectors to dominate the world market.
Less quantitative forms of a similar "infant industry" argument against totally free trade have been advanced by trade theorists since at least 1848 (see: History of free trade).
The value of protecting "infant industries" has been defended at least since the 18th century; for example, Alexander Hamilton proposed in 1791 that this be the basis for US trade policy. What was "new" in new trade theory was the use of mathematical economics to model the increasing returns to scale, and especially the use of the network effect to argue that the formation of important industries was path dependent in a way which industrial planning and judicious tariffs might control.
The models developed predicted the national specialization-by-industry observed in the industrial world (movies in Hollywood, watches in Switzerland, etc.). The model also showed how path-dependent industrial concentrations can sometimes lead to monopolistic competition or even situations of oligopoly.
Some economists, such as Ha-Joon Chang, had argued that protectionist policies had facilitated the development of the Japanese auto industries in the 1950s, when quotas and regulations prevented import competition. Japanese companies were encouraged to import foreign production technology but were required to produce 90% of parts domestically within five years. Japanese consumers suffered in the short term by being unable to buy superior vehicles produced by the world market, but eventually gained by having a local industry that could out-compete their international rivals.