The treaty was planned to enter into force in January 2009, after all member states ratified it.

Ireland, however, held a referendum on the Lisbon Treaty—the only EU member state to do so. And the treaty was rejected there in June 2008, throwing the EU into the crisis once again.

To allay doubts among the Irish people that the treaty may have been harmful to their national interests and sovereignty, the other 26 EU member states offered significant concessions.

In the end, the treaty was passed in the second referendum that was held more than one year later on October 2, 2009.

Later, on October 10, Polish President Lech Kaczynski officially signed the treaty, followed by Czech President Vaclav Klaus on November 3. Until then, all the 27 member states completed the ratification procedures.

Significant changes to come

The Lisbon Treaty's entry into force on December 1 has been a landmark event in the EU's integration process. Indeed, it will herald a series of significant changes for the EU.

The most important change is that EU states will now possess new ability to act together in the international arena through the creation of two top posts—the president of the European Council, and the high representative for foreign affairs and security policy.

After hard and complicated negotiations, Belgian Prime Minister Herman Van Rompuy and the EU Trade Commissioner from Britain Catherine Ashton were appointed to take the posts respectively.

This organizational reform will help strengthen the EU's leadership, while enhancing its decision-making efficiency and maintaining the continuity and stability of its policies. Meanwhile, the decision making of its foreign policies will get more centralized and unified thanks to the reform.

The predictability and sustainability of its foreign policies will also be promoted. The EU will be able to speak with one single voice, thus boosting its influence on the world stage.

Another big change is that EU institutions—including the European Commission, the European Council and the European Parliament—will be more independent of the member states.

The Lisbon Treaty, moreover, will see some 40 new policy areas to be decided on by qualified majority voting at the European Council, rather than by unanimity. This will greatly enhance the efficiency, and strengthen the supranational elements of the council.

The European Parliament, likewise, will enjoy bigger power in legislation, budget and political supervision. With the Lisbon Treaty entering into force, the EU will also finally have a legal personality. This will promote the role of the EU as an international player.

Although there are still quite a few contradictory articles in the Lisbon Treaty—some of which may raise uncertainties for its implementation in the future—its adoption has nonetheless ended the EU's long lasting constitutional crisis, while bringing it back to the center of the world stage.

The Lisbon Treaty's entry into force and the creation of the two top posts indicate that the European political integration has entered a new period. It also signals new opportunities for the development of Sino-European relations.

As the treaty is implemented, EU member states will be more coordinated in their dealings in the arena of Sino-European relations. Bilateral platforms and mechanisms between China and the EU will become more effective and equivalent, for instance, thus making it easier for the member states to adopt consistent policies toward China with the coordination of the EU.

All these can promote the EU's cooperation with China. Overall, both the EU and China should seize these opportunities to promote a better and quicker development of their strategic partnership.

The author is a professor with the Institute of International Relations at the China Foreign Affairs University