A free trade agreement is a pact between two or more nations to reduce barriers to trade between imports and exports. Under a free trade policy, goods and services can be bought and sold across international borders without government tariffs, quotas, subsidies or bans. The creation of free trade zones is seen as an exception to the most privileged principle of the World Trade Organization (WTO), since the preferences of the parties to the exclusive granting of a free trade area go beyond their accession obligations.  Although GATT Article XXIV authorizes WTO members to establish free trade zones or to conclude interim agreements necessary for their establishment, there are several conditions relating to free trade zones or interim agreements leading to the creation of free trade zones. In the first two decades of the agreement, regional trade increased from about $290 billion in 1993 to more than $1 trillion in 2016. Critics are divided on the net impact on the U.S. economy, but some estimates amount to 15,000 a year. As soon as the agreements go beyond the regional level, they need help. The World Trade Organization intervenes at this stage. This international body contributes to the negotiation and implementation of global trade agreements. This view became popular for the first time in 1817 by the economist David Ricardo in his book On the Principles of Political Economy and Taxation. He argued that free trade broadens diversity and reduces the prices of goods available in a nation, while making a better part of its own resources, knowledge and specialized skills. Unlike a customs union, parties to a free trade area do not maintain common external tariffs, which means that they apply different tariffs and other measures on non-members.
This function allows non-parties to free themselves as part of a free trade agreement by entering the market with the lowest external tariffs. Such a risk requires the introduction of rules for determining which products originate may be preferred under a free trade agreement, which is not necessary for the establishment of a customs union.  In principle, there is a minimum processing time leading to a «substantial processing» of the products, so they can be considered original products.