Four Reasons Proliferation Stayed Limited

Contrary to 1960s predictions of 15-25 nuclear states, only nine exist because of four reasons: superpower security guarantees that bought off would-be proliferators, a system of international law and export controls raising costs, occasional counter-proliferation through military action or sanctions, and an underrated set of anti-nuclear norms causing elites to view the weapons as immoral liabilities rather than assets.