Integrationist ideas arise in the post-colonial era, at the end of the 18th century and during the 19th century, to boost trade and the economy; the newly independent nations sought to create their own identity, on the basis of consolidating historical, political and cultural ties. The awakening of Latin American consciousness, coincided in this way, with the discovery of the consequences that brought to the countries of the region, the new forms of economic and political penetration of the capitalist powers in their imperialist stage (Fernández, 2014).

In the particular case of MERCOSUR Customs, its beginnings go back to the times of the Spanish and Portuguese conquest and colonization (^{Juárez and Conde, 1967}). During the course of the 19th century until World War I, economic policies that promote free trade, the free movement of goods, and the non-intervention of the State in economic affairs are imposed in the West (Laissez faire et laissez passer, le monde goes from lui même), limiting its function to safeguard order and security. In customs matters, protectionist practices were eliminated, internal controls were abolished, and tariffs were reduced to the point of not affecting free movement. Arrived at the twentieth century, the effects of the economic crisis of the thirties, brought with it the loss of vigor in commercial activities worldwide, the redesign of the State's economic policy through the intervention and regulation of markets, what which led to the dismantling of the liberal model and its replacement by one of a protectionist nature with a strong state presence in foreign trade activities (^{Juárez and Conde, 1967}).

The reimplementation of protectionist tariff measures and the establishment of direct restrictions on foreign trade meant for customs customs the marginalization of tariffs as financial instruments of fiscal support and their substitution by internal taxes, opting States for the signing of bilateral agreements between countries as new way of negotiating by setting special and preferential tariff rates under the principle of reciprocity ("bilateralism") that extended until the end of World War II. Concluded world conflicts, returns to free trade ideas applied in the nineteenth and early twentieth centuries (now called "neoliberalism") leading to the progressive liberalization of world trade, "multilateralism" (replacing bilateralism), and the creation of International Organizations that order and regulate world foreign trade. Thus, the World Bank, the International Monetary Fund, the International Trade Organization, which subsequently resulted in the General Agreement on Tariffs and Trade (GATT) and then became what is now known as the World Trade Organization ( WTO) and the Customs Cooperation Council, today the World Customs Organization.

The need of the countries of the South American cone to consolidate a customs alliance is old. In 1941 the Agreement of the countries of the La Plata River was signed to form a customs block. This Brazilian initiative failed to materialize, because the Japanese attack on Pearl Harbor put the Western Hemisphere on the scene of World War II. In the following decade, Brazilian President Juscelino ^{Kubitschek launched Operation Pan American (1958}), proposing to redefine South America's relations with the power of the North. “I verify that in Brazil - and I believe that in the other countries of the continent - the consciousness matured that it is no longer convenient to form a mere choral ensemble, a rearguard without character, a simple frame fund” (Kubitschek 1958, quoted by Moniz Bandiera, sf).

But, if we move to more recent times, in 1997 the WTO visualized Mercosur as an ambitious project that made important progress towards becoming a Customs Union. Considerable progress has been made in achieving a customs union and has gone even further, namely, towards a common market (although not the single market model of the European Union), but there are several areas in which there is still they can make progress (^{Laird, 1997}, p. 2).

The idea of ​​Mercosur has its origin in the Program of Integration and Economic Cooperation (PICE) signed in 1985 between Brazil and Argentina. This effort would later be consolidated in the Integration, Cooperation and Development Treaty of 1988. To realize these ideas, in 1990 the Buenos Aires Act was signed, which accelerates the deadlines for the establishment of a Free Trade Zone between Brazil and Argentina. In 1991, Uruguay and Paraguay adhere to the achievements that Brazil and Argentina had achieved in terms of integration. Then, on March 26 of that year, the Treaty of Asunción is signed, giving rise to Mercosur. Subsequently, the Economic Complementation Agreement No. 18 (ACE No. 18) is signed, within the framework of the Latin American Integration Association (ALADI), with which the WTO was notified, under the Enabling Clause, about the creation del Mercosur (^{Cardona, 2013}).

The economy of Paraguay was characterized by the relevance of maintaining a fluid trade avoiding obstacles of all kinds, this need is further evidenced by being a Mediterranean country. That is why throughout its history it was part of numerous processes of integration at the regional level and of negotiations at the international level many times under the Most Favored Nation clause with the General Agreement on Tariffs and Trade (GATT), today World Trade Organization (WTO).

In response to the situation in the early 1990s, Paraguay, together with Brazil, Argentina and Uruguay, decided to initiate an integration process with a view to forming a common market. Thus, on March 26, 1991, the Southern Common Market (MERCOSUR) treaty was signed.

Considering the high exports to Brazil and Argentina, mainly, they have been developing with greater or lesser difficulty. The idea of ​​an integration that supposes a tariff between the States Parties, would allow to enter a product with zero tariff, during the denominated stage, zone of free commerce.

Therefore, the next stage that was intended to take place before 1995 was that of customs union. The inconvenience arises during this stage, when after adjustments to have a common external tariff by the four States, it fails to materialize. Many scholars of economic integration, such as ^{Laird, 1997} and ^{Bouzas, 2003} refer to this process as an imperfect customs union or incomplete customs union since they fail to meet the objectives of a Perfect Customs Union.

It should be remembered that the goal to reach the stage of a common market, within the integration to the MERCOSUR block, was set for 1994. In this process the stage prior to this one, that of the customs union, was reached. With the passing of the years, this stage could not be concluded, considered therefore as imperfect customs union or incomplete customs union. Like any process, it implies constant negotiations between the States Parties, whose parity is evidenced taking into account that all are in equal conditions at the moment of agreeing something; independent of the obvious asymmetries between the countries that comprise it, based mainly on its Gross Domestic Product.

MERCOSUR must undoubtedly focus on improving the free trade area, especially with the reduction of non-tariff barriers, the deepening of negotiations of other standards (technical, sanitary, phytosanitary, customs, etc.) that promote free trade. transit of merchandise.

The bloc must assume that it is necessary to implement definitive substantial flexibilities and reforms, to start a new stage that makes the integration process a more modern instrument that serves national and regional interests in a new and increasingly complex international context and that it does not admit rigid models that prevent the necessary reaction of the States to the new international trends.

Taking into account that the European Union (EU) is the best reference of the existing AU and this implies: absence of customs duties at the borders between the member countries of the block (full freedom in the movement of goods within the UA) , common customs duties on imports from outside the EU, common rules of origin for products imported from third countries, and a common definition of customs value; Considering these starting parameters, MERCOSUR has failed to consolidate itself as a Customs Union per se, rather it would come to demonstrate its imperfections as a mechanism of total integration, however MERCOSUR has made strong progress in consolidating itself as a free trade zone but from a perspective economic, a common tariff can be measured, among other indicators, through the strengthening of its intra-regional trade. An increase in commercial interdependence allows us to assume that relations between nations that are members of a block have a positive impact on economic growth and job creation.

In the case of Mercosur and Paraguay, the statistical evidence is favorable, since exports have grown steadily, this may be due to the positive momentum since the year of the signing of the Montevideo Treaty. Consequently, it is clear that Mercosur is a very important export market for Paraguay, but, at the same time, in terms of regions, the statistics are not very encouraging, since MERCOSUR has only maintained 15% of intra-regional trade and 85% of extraregions trade.

Currently, more than 90% of Paraguayan exports are commodities, which explains why their destination is mainly Europe, China and the USA. UU, but many of these products also go to MERCOSUR countries and then become value-added products.

In the case of Paraguay, a greater dependence on its intra-regional trade is evident. According to the Observatory of International Economy (OBEI), what stands out is that in the last 7 years Brazil has grown as a destination for Paraguayan exports, to the detriment of Argentine participation. In 2005, that country bought 320 million dollars from Paraguay, a figure that reached 1,062 million for 2012 and 2,800 million for 2019, representing more than 80% of Paraguayan exports to Mercosur (OBEI, 2016).

In commercial terms, MERCOSUR is a good free trade zone mechanism, but it has not been consolidated as a Customs Union, probably the diverse structure and economic size of the partners, partly explain the disagreements and barriers that do not they allow Mercosur to advance in its integration project. However, the figures show that there is great intra-regional commercial potential, since large economies have a non-negligible manufacturing industry, which needs markets and can hardly position their products in the powers of Europe and North America.

Undoubtedly, integration is the infallible recipe for the achievement of the integral development of the countries and there is almost no other formula to refute the commonality as a method of achieving objectives in international trade and social development of the countries that opt ​​for the integration.

Mercosur is considered one of the great trade agreements of the planet. Even the industrializing dynamics of its two great partners (Brazil and Argentina), strengthens the postulates that affirm that the block has conditions to be inserted more strongly in the global circuits of commerce, at the same time that it has the weight to be a relevant negotiator in The multilateral forums.

Probably the diverse structure and the economic size of the associates, partly explain the disagreements and barriers that do not allow Mercosur to advance in its integrationist project. The goal should be to consolidate a Customs Union not only as an engine for the intra-regional trade boom, but to create one of the largest customs territories on the planet. Mercosur could be a larger negotiator in the WTO, strengthening subregional aspirations for more free global trade in agricultural and manufactured goods.

From a strictly economic perspective, if MERCOSUR were able to consolidate itself as a perfect customs union, it would be possible to strengthen intra-regional trade that reflects an increase in commercial interdependence, which would allow us to assume that relations between nations that are members of a block positively impact economic growth and the generation of jobs, the strengthening of regional industries and the expansion of their endogenous markets.

From a social perspective, integration must consider the principle of solidarity between countries considering the fact that the member countries have marked differences marked in the fact that more developed countries obtain advantages over their less developed peers, so it is It is necessary to homogenize the space to be integrated, which is only possible through the solidarity concretized mainly through aid and financial cooperation and convergence funds in order to reduce inequalities, cooperation must take place in all areas: cultural, economic, scientific, commercial, technological and educational.