We argue that bank performance—measured in terms of credit provision and financial stability—depends on the particular mix of social purpose and market discipline - underpinning banks’ behavior. Economic nationalism centered on striving for policy autonomy imbues banks with political goals, including serving the national economy. Economic nationalism is therefore the source of social purpose. But we argue that for optimal bank performance, economic nationalism and social purpose must be constrained. Market discipline in tension with social purpose prevents banks from engaging in excesses—including related-party lending or imprudent risk assumption. We find that countries with elements of nationalism in combination with robust political competition are most likely to have domestic banks that provide both sufficient credit financial stability. But we also find that this optimal mix of social purpose and market authority had by 2016 become increasingly challenging and rare in Europe’s peripheral states.