From 1945 to 1991, the preeminent source of security in international affairs was the nuclear bomb. The few nations that openly had credible means of delivery – the United States, the USSR, Britain, France, and China – successfully deterred physical aggression by another state against their homelands.
Their collective experience and the perceived frailties of those states not possessing the bomb eventually created the following narrative: Nuclear weapons provide security to states while the lack of them leaves a country vulnerable.
In this setting, two diametrically opposing trends were born. The first was driven by states that viewed their circumstances as so perilous that the only alleviating factor would be acquiring the bomb.
The second was the goal of states either already possessing nuclear weapons or firmly protected in a larger security organization (e.g., NATO) to prevent the spread of atomic weapons.