International trade barriers
'Mercantilism' or Trade Theory was prevalent in 17th & 18th centuries which determined patterns of International trade & gains from trade. The barriers to International Trade are generally called Tariff Barriers and Non-Tariff Barriers (TBs & NTBs). Regional Integration Agreements (RIA) were basically formed so as to reduce Trade barriers between member nations. The formations of subsequent RIAs, i.e. from "Free Trade" to "Customs Union (eg. SAARC)" to "Common Market" to "Economic/Political Union (eg. European Union)" went on reducing trade barriers with members and outside nations for developing good economic ties and International trade relations.