Many critics of NAFTA saw the agreement as a radical experiment developed by influential multinationals who wanted to increase their profits at the expense of ordinary citizens of the countries concerned. Opposition groups argued that the horizontal rules imposed by nafta could undermine local governments by preventing them from enacting laws or regulations to protect the public interest. Critics also argued that the treaty would lead to a significant deterioration in environmental and health standards, promote privatization and deregulation of essential public services, and supplant family farmers in the signatory countries. Multilateral trade liberalization, in which all countries reduce their trade barriers at the same time, is the best way to promote trade on the basis of comparative advantages. However, countries can abuse the system by adopting a beggar-neighbouring policy of Thy  A good explanation for this sentence, which shows a hypothetical trade relationship between two countries, is available under faculty.washington.edu/danby/bls324/trade/hos.html. Little has happened in the labour market, which has significantly changed the outcome in each country participating in the treaty. Because of the immigration restrictions, the wage gap between Mexico, on the one hand, and the United States and Canada, on the other, has not decreased. The lack of infrastructure in Mexico has led many U.S. and Canadian firms to choose not to invest directly in Mexico. As a result, there were no significant job losses in the United States and Canada and there were no environmental disasters due to industrialization in Mexico. Access to other markets plays an important role in this business model, where comparative advantages can be created. In the absence of free trade, it is extremely costly for a government to subsidize a new entrant, as the subsidy must be relaxed, both to overcome the barriers of foreign trade and to stimulate the domestic producer.
The WTO-U.S. free trade agreements also play an important role in establishing rules governing what a country can do in many areas to create comparative advantages; For example, the grant code limits the nature of the subsidies that governments can provide. In addition, some products do not use the same production factors over their life cycle.  For example, when computers were first introduced, they were incredibly capital-intensive and needed a highly skilled workforce. Over time, as the volume increased, costs decreased and computers were mass-produced. In the beginning, the United States had a comparative advantage in production; but today, while computers are mass-produced by relatively unskilled labour, the comparative advantage has shifted to countries where labour is plentiful and cheap. And other products can use different production factors in different countries. For example, cotton production is very mechanized in the United States, but it is very laborious in Africa. The fact that the factors of production may change does not negate the comparative advantage theory; it simply means that the package of products that a nation can produce relatively effectively can change only its trading partners.
 Bertil Ohlin published this theory in 1933. A brief explanation of the Heckscher-Ohlin theory can be nobelprize.org/educational_games/economics/trade/ohlin.html.