A society experiences external stability when it is able to protect its territorial borders. Without adequate protection of its territorial boundaries a nation or state is inherently unstable, especially if it juxtaposed to other nations that are suffering from high levels of internal instability.
This is one of the main reasons that European nations came together after World War II to create the European Community. They recognised that by cooperating with each other to form a higher order economic entity, they would increase their own internal stability and reduce the potential for a third World War. This is also one of the main reasons why the former USSR created a communist block of buffer countries between itself and the rest of Europe. This was a strategy to protect its borders.
Another strategy for achieving external stability is for like-minded nations or states to bond together in strategic alliances or as allies to overcome a common foe. This is what happened in the American Revolutionary War (1775 to 1783), and in Europe in World War I and World War II.
Thus, the natural response to a common external threat or any issue that compromises the stability of a number of communities or nations in close proximity to each other is for those communities or nations to cooperate with each other in a strategic alliance of a temporary or permanent nature, and create a higher order entity working for the common good.
Chapter 23: Societal Consciousness