early American history strikes me as being punctuated by periods where individual liberty was the highest value. The frontier/westward expansion, for example. The constitution itself seems hinged on optimising for personal liberty by balancing "freedom to" and "freedom from" liberties.

I always thought of personal liberty as the value from which other values derive. For example, the law exists to protect our rights (the right to life and the right to property being the most obvious examples) from bad actors. Social welfare and socialised healthcare restrict the damage that personal catastrophe and random chance can do to our freedoms.

the commitment of the predominant culture.

I'm always less inclined to believe that it's a few powerful people, and more inclined to think it's a cultural war between memes (in the Dawkins sense). People are driven by ideas. If powerful people are contributing to a cause it's probably because they are under the influence of a meme. That, or a more Machiavellian reasoning like trying to purchase social capital.