5. Birth of Schengen Agreement

On June 14, 1985, the Schengen Agreement on the elimination of border controls is signed by Belgium, Germany, France, Luxembourg and the Netherlands in Schengen (Luxembourg).

The Schengen Agreement gradually allows people to travel without having their passports checked at internal borders. Implementation of the Schengen Agreement starts later, in 1995 and now covers most European countries excluding UK.

6. The Maastricht Treaty

On 1993 November 1st, the Maastricht Treaty comes into force creating the European Union based on an enlarged 'Community' pillar. It creates the economic and monetary union and sets two new pillars: common foreign and security policy (CFSP) and cooperation in the fields of justice and home affairs .The European Council acquires a formal status in the Treaty of Maastricht. It is defined as providing the impetus and general political guidelines for the EU's development. The Maastricht Treaty also starts the move towards the euro and launches Common Foreign and Security Policy (CFSP).

7. Euro and euro zone

The European Council endorses the creation of the Eurogroup, an informal body that brings together the finance ministers of countries whose currency is the euro. The first Eurogroup meeting is held on 4 June 1998 and on 1 January 2002 the euro starts circulation as banknotes and coins, replacing national currencies. The Euro zone now consists of 18 EU members.

8. The Treaty of Lisbon: "European Constitution"

In late 2009, the Treaty of Lisbon enters into force, reforming the structure of the EU and the way in which it functions. The European Council becomes a fully-fledged institution with its own President. And the treaty also established the European External Action Service, responsible for the union's foreign and defense affairs.

9. Debt Crisis

The sovereignty debt crisis in European Union follows the 2008-09 global financial crisis originating from the US. The upheavals, however, force the bloc to strengthen its financial firewall and institutional construction, seeing the births of the European Stability Mechanism and the EU Banking Union. To revive its economy, European Commission introduced a three-year 315-billion-euro investment scheme.

10. Mutli-fold challenges

Currently, apart from Brexit, European Union has faced tremendous challenges of influx of migrants in millions from West Asia and North Africa, its relationship with Russia due to Ukraine crisis and domestically, urgency in boosting economic growth and rise of the right political force and populists. Greece has also plunged into financial crisis, requiring a series of bailouts.

To contact the reporter: fujing@chinadaily.com