Where Has Our Sense of Community Gone?

Short answer--damned if I know.

Longer answer--gone with dissolution of the Soviet Union. For my entire lifetime the US has had adversaries, first the Axis, then USSR. After 1991 we've had no such adversaries.  Brief flirtations with Japan as an economic rival, with Bush's Axis of Evil supporting terrorism, and later China as a rising rival don't match the threats those mid-century adversaries seemed to pose.  Today we're seeing with Russia's invasion of Ukraine we're seeing a resurgence of unity, of national feeling, etc. both in Congress and the country.

So--my answer: sense of community vanished with our enemies.