During the Cold War, the United States supported selective nuclear proliferation as a means of deterring a Soviet invasion of Europe. The Russians might not believe that the United States would trade Berlin for New York, but they might find a British or French threat more credible.
Washington did not pursue the same strategy in Asia. Although Japan could easily match Britain or France in economic power and technological sophistication, the United States didn’t see fit to support Japanese nuclearization. Instead, the United States quashed Japanese nuclear ambitions whenever they appeared.