Most measures of country power in international relations focus on economic factors (e.g. GDP, energy production), military expenditures and personnel, demographic, or a combination of these broad economic, military, and demographic factors. 

I created a country-year measure of military power that focuses primarily on weapons systems.  The indicator, Material Military Power (MMP), includes naval weapons, air weapons, land weapons, ballistic missiles and nuclear weapons. 

For most uses, MMP has more validity than alternative measures.  

A manuscript on MMP is forthcoming in the Journal of Peace Research. You can read an early version here:   

Material Military Power manuscript

MMP (Material Military Power indicator and components). For the full data, go to the Harvard dataverse.