That would depend entirely on how you define the word "strong". Before America became an Empire, she was "strong" in the sense that her people and her "small r" republican virtues gave her strength. Being a huge "superpower" with a "place in the world" second to none, might be things that one would point to as evidence of America's strength. I wouldn't.
I would submit that the events surrounding September 11, show us that this "strong" Empire that we still call America is very, very weak. The true strength of America resides in the American people and that strength will be here regardless of how "important" we are in the world or how grandiose our military-industrial complex is.
America was a good country long before it was a "great" country. One should not confuse the trappings of State and Empire with "greatness" as I believe far too many conservatives -- from Kristolites to Keyesters -- do far too often.