After the cold war, Europe has been shaping a new security system that consists of security organisations, such as UN, Nato, WEU, EU, OSCE and CE. During the cold war, WEU was developing in the shadow of Nato, while EC existed mainly as an economic-political entity of West European countries. By establishing Common foreign and security policy and fusion with WEU, EU became active in security and military fields as well. However, as proved by the Nato military intervention in Kosovo, the EU's great ambition in these fields could not cover its military inferiority towards Nato (USA). The military ambitions of EU have also complicated its relations with Nato. However, the terrorist attack on USA (11th September 2001), as the worst act of a sort in human history, and the commencement of common fight against terrorism, have contributed to the strengthening the alliance and possibly to faster settlement of relations among USA, EU and European members of Nato.