The Alliance was founded on 4 April 1949, as a system of collective defense concerning the metropolitan territory of the Member States, on the basis of the criterion of mutual aid: in the case of an armed assault outside one or more members all the others are committed to intervene to ensure the safety of the attacked members. The answer is not automatic but must be preceded by political consultations. In 1969, NATO took on unlimited duration (with the power of withdrawal by members).In 1991 he established a Partnership for Peace with Russia and began a process of enlargement to the East, including all the countries of the Ex War Pact, the three Baltic countries and some countries of the former Yugoslavia. At the same time, cooperation agreements have been initiated with Ukraine, Georgia, Azerbaijan and Mongolia. In addition, starting in 1999, on the occasion of its 50th anniversary, for the first time it intervened militarily outside its area of competence, against Serbia and against the Taliban in Afghanistan.
Today, NATO continues to be the world's leading collective security system, with the highest degree of standardization of its national forces and carrying out functions to contain Russian military and political influence in Western Europe (small NATO contingents have been deployed in Iceland, Poland and the Baltics). However, the Alliance also presents internal contradictions: Turkey's uncertain political position, following Ankara's veiled accusations towards NATO that it supported the failed 2017 coup and the purchase of missiles from Russia; Trump's call with Europe for more contributions to the common budget and finally, the start of other systems of cooperation between European countries, such as the Trimarium,a pact established in 2018, essentially of an economic nature, between the countries of the old Habsburg Empire. This groupes twelve countries, Poland, Hungary, Czech Republic, Slovakia, Estonia, Latvia, Lithuania, Bulgaria, Romania, Austria, Slovenia, Croatia, touching the Baltic Sea, the Black Sea and the Adriatic.