NATO expands

All but Slovenia had been part of the Warsaw pact - aligned with the Soviet Union during the cold war.

This is the second expansion in five years to take in members of the old Soviet aligned bloc. In 1999 the Czech Republic, Hungary and Poland became members.

However this latest expansion could well prove one of the most controversial to date. The Russian government in recent weeks has demanded explanations for the presence of NATO troops in the Baltic republics.

NATO has said that it reserves the right to police the skies over any of its member states.

The coming years will also be testing ones for the alliance as new states may be called upon to take on ever more ‘out of area’ tasks, with NATO considering a role in Iraq as well as its recent take-over in Afghanistan.

Like the EU’s enlargement, NATO will face significant challenges in the way it operates, with ever more voices round the table clamouring to make their voice heard.

Relations with the EU will also be under the spotlight.

As the European Union seeks to increase its security capabilities, so the role of NATO in Europe comes under scrutiny and compatibility between the two organisations' defence goals.

The alliance, formed just after the Second World War, now boasts 26 members.