NATO is Established.

The North Atlantic Treaty, which established the North Atlantic Treaty Organization (NATO), an intergovernmental military alliance, came into effect on this day. The Treaty, which was signed on April 4, 1949 in Washington DC, created a collective defense system, where an attack on one member is considered an attack on all the other signatories. Initially, the treaty was signed by 12 countries – Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, United Kingdom, and United States. Today, membership has increased from the original 12 to 28.

Source