November 2018 marked a quarter of a century since the adoption of the Treaty on European Union (TEU), signed in Maastricht and thereafter referred to as the Maastricht Treaty.
It became one of the most important agreements in the history of Europe, creating the European Union we know today and forming the backbone of many of the bloc's rules and regulations.
Here, we'll take a closer look at the Maastricht Treaty, its legacy in the 25 years since its adoption - and its future as the EU prepares to go forward without Britain under its guardianship.
Background on the Maastricht Treaty
The treaty was signed on February 7th 1992 by 12 countries: Belgium, Denmark, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain and the United Kingdom.
It came into force on November 1st 1993 and since then, a further 16 nations have joined the EU and adopted the rules set out in the Maastricht Treaty and in the treaties that followed later.
Maastricht added two new areas to the existing European Community - justice and home affairs and a common foreign and security policy - establishing the famous three-pillar structure that lasted until the Lisbon Treaty in 2009.
It gave the people of the 12 member states European citizenship and the right to move and live in any EU state, as well as to vote in European and local elections in any country.
Under Maastricht, members were also committed to implementing common foreign and security policies and encouraged to cooperate on other issues, including the environment and policing.
Furthermore, it applied monetarist control of inflation and imposed limits on government public spending, dictated through debt and deficit as a proportion of gross domestic product.
The importance of the Maastricht Treaty
The importance of the Maastricht Treaty cannot be overstated. Effectively, it created the EU, integrating a unified Germany into the fold, and laid the foundations for a common currency, the Euro.
Its reforms restructured the then-European Community by establishing a political union and strengthening economic integration through the Economic and Monetary Union. It also helped to restabilise a frequently segregated Europe after the Cold War.
Maastricht helped to design the architecture of the EU and European leaders have since agreed additional steps to further promote European integration, including the 1997 Stability and Growth Pact, the Single Supervisory Mechanism and the Single Resolution Board.
For the first time, there had been an important change in institutional balance by giving more powers to the European Parliament, aimed at widening democratic accountability in the European decision-making process.
Brexit and the future of the Treaty on European Union
Since Britain's referendum triggered Article 50 and set out the road to Brexit, the future of harmony in the EU has been called into question.
A recent study commissioned by the European Parliament's Policy Department for Citizens' Rights and Constitutional Affairs called the UK's withdrawal from the EU "an unprecedented development in European integration".
However, it pointed out that in many areas, the UK has not been in support of EU integration policies and called it "an awkward partner" with "a transactional approach to EU membership".
It said that the EU is unlikely to disintegrate because of the UK's withdrawal, but did acknowledge that "significant systemic challenges remain" and that the EU "will be losing a strong and self-confident supporter of the single market", while other member states such as Sweden "will also be losing a key ally".
In GDP terms, Britain's departure is the equivalent of the EU losing the 19 smallest member states, so there is sure to be some shift in the balance of power and the direction of European integration.
The report concluded by saying that the effect of Brexit will be determined by two effects: the UK's success or failure outside the EU and how this is perceived by other member states; and the EU's ability to cope and demonstrate that it is still effective as laid out in the Maastricht Treaty.
It added: "The UK's withdrawal is an opportunity and a risk to the remaining members of the EU. [It] is not a short-term process, but one which will have some influence on the EU for at least a decade or more."
If the EU can continue to be unified after Brexit and the other challenges it faces, it may be that the effects of the Maastricht Treaty remain relevant for another 25 years.