What advantage did European countries gain by allying with a super power?

Western Europe had a distinct advantage in alliance with the United States and through NATO. American defense expenditures coupled with the Marshal Plan for reconstructing Europe allowed them to focus on social welfare rather then rearmament. The provisions of a American nuclear umbrella created further reassurances to deterring a Soviet land invasion into Western Europe. That being said France under Du Gaulle committed to their own independent nuclear deterrent.