Tuesday, August 3, 1999 Published at 14:55 GMT 15:55 UK
Nato's Cold War roots
Nato has 19 members; Switzerland and Austria are neutral
Fifty years ago, unsettled by a war which had rocked political and economic confidence, the West desperately needed security.
Their solution was the North Atlantic Treaty Organisation.
There were 10 European and two North American founder members: the US, Canada, Belgium, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal and the UK.
Nato members were united against Communism and had a common commitment to protection. The fundamental principle of the Treaty, which remains to this day, is Article 5: "an armed attack against one or more of them in Europe or North America shall be considered an attack against them all."
From the start, Nato was open to accepting new members - and still is. Greece and Turkey joined the alliance in 1952, West Germany in 1955 (the reunited Germany officially acceeded in 1990) and Spain joined in 1982.
The original purpose of the grouping was to defend Western interests through the Cold War.
A command system for possible war-time use was established and the Military Committee became a powerful body.
Huge funds were poured into back-up for Nato forces - bases, airfields, depots and communication networks - to deter Soviet or Warsaw Pact expansion. US nuclear weapons were also stationed in Western Europe.
The conflict came to a head in 1966 when French president Charles De Gaulle announced France would withdraw from the military structure in protest at dominance of US commanders. Nato forces were required to leave the country and headquarters were moved to Mons, Belgium.
Today, France remains only part the political structure of the alliance in case of "unprovoked aggression". It continues to emphasise the independence of its nuclear armoury and foreign policy.
A new era
Nato's greatest triumph is considered to be winning the Cold War. But the collapse of the USSR in 1991 and the sweeping away of the Iron Curtain left the allies with no obvious mission.
At the 1991 Rome Summit, co-operation Central and Eastern European countries and the former USSR became a top priority.
Hungary, the Czech Republic and Poland became new members, moving Nato's borders an estimated 400 miles eastwards and adding an extra 350,000 servicemen. (They officially joined in March.)
In response to the decreased threat, numbers and readiness of Nato troops have been vastly reduced. This includes a 25% cut in the number of ground combat units and a reduction of over 45% in the peace-time strength of land forces in the Central Region.
Stockpiles of nuclear weapons are now only one-fifth of their total in 1990.
Dilemmas over Kosovo
The Kosovo crisis has given the alliance a new mission - and a political and military headache. Nato's response to Yugoslav President Milosevic was a product of its history - aiming to defend European countries' borders.
This is a test of the Nato of the 21st century", said the US Secretary of State, Madeleine Albright.