Why maastricht treaty is so important?

Answer 1

Under the heading of The Maastricht Treaty on Wikipedia, it gives this explanation about the imprtance of this treaty.

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The treaty led to the creation of the euro currency, and created what is commonly referred to as the pillar structure of the European Union. This conception of the Union divides it into the European Community (EC) pillar, the Common Foreign and Security Policy (CFSP) pillar, and the Justice and Home Affairs (JHA) pillar. The latter two pillars are intergovernmental policy areas, where the power of member-states is at its greatest extent, whilst under the European Community pillar the Union's supra-national institutions - the Commission, the European Parliament and the Court of Justice - have the most power. All three pillars were the extensions of pre-existing policy structures. The European Community pillar was the continuation of the European Economic Community with the "Economic" being dropped from the name to represent the wider policy base given by the Maastricht Treaty. Coordination in foreign policy had taken place since the beginning of the 1970s under the name of European Political Cooperation (EPC), which had been written into the treaties by the Single European Act but not as a part of the EEC. While the Justice and Home Affairs pillar extended cooperation in law enforcement, criminal justice, asylum, and Immigration and judicial cooperation in civil matters, some of these areas had already been subject to intergovernmental cooperation under the Schengen Implementation Convention of 1990.