Since the beginning of the 20th century, several hundred bilateral THPs have been signed. The Canada Research Chair in International Political Economy`s TREND project lists approximately 700 trade agreements, the vast majority of which are bilateral.  Economic integration can be part of five additives in the global landscape: these tariff preferences have created many divergences from the principle of normal trade relations, namely that members of the World Trade Organization (WTO) should apply the same duty to imports from other WTO members.  A preferential trade zone (including preferential trade agreements, PTA) is a trading bloc that gives preferential access to certain products from participating countries. This requires a reduction in tariffs, but not in their total abolition. A ZEP can be implemented through a trade pact. This is the first step in economic integration. The border between a EPZ and a Free Trade Area (EEA) can be blurred, as almost all ATPs have the main objective of becoming a free trade agreement in accordance with the General Agreement on Tariffs and Trade. Given the recent proliferation of bilateral TTPs and the emergence of mega-PTAs (broad regional trade agreements such as the Transatlantic Trade and Investment Partnership (TTIP) or the Trans-Pacific Partnership (TPP), a global trading system managed exclusively under the WTO now seems unrealistic and the interactions between trade systems must be taken into account.
The increasing complexity of the international trading system resulting from the proliferation of EPZs should be taken into account when considering the choice of countries or regions used by countries or regions to promote their trade relations and environmental agendas.  ATPs have grown rapidly; In the 1990s, there were just over 100 PTAs. In 2014, there were more than 700.  With increasing economic integration, the complexity of the rules is also increasing. These are a number of rules, enforcement and arbitration mechanisms to ensure that importers and exporters comply with the rules. Complexity has a cost that can compromise the competitiveness of territories in the context of economic integration, as it reduces the flexibility of national policies.