Theory of Samuelson and Stolper
In the middle of XX century. (1948) American economist Paul Samuelson and W. Stolper improved the Heckscher - Ohlin, providing that if the homogeneity of the factors of production, identity, technology, perfect competition and full mobility of the international exchange of goods equalizes the price of production factors between countries. The authors based their concept on the model of Ricardo to Heckscher and Ohlin additions and view trade not just as a mutually beneficial exchange, but also as a means to reduce the gap in development levels between countries.