What is New Trade Theory?

Legal Definition
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).
-- Wikipedia