Common religion, math, language???
The problem with megalithic structures is, they often appear to be made by a common culture, but there’s no record left by the builders, anywhere these things are found. Another problem is, maybe they aren’t from a common culture, but just look so similar because they are often unshaped stones stood on end or piled up, not a difficult idea to come up with.
The crowning phase of Stonehenge appears to have been followed fairly closely by abandonment of the site, with no further development during the last century or so of use. The last construction on the site was about 1600 BC. By contrast, Mystery Hill a.k.a. “America’s Stonehenge” in New Hampshire yielded radiocarbon results of 2000 BC (iow, it wasn’t built during colonial times, unless they had time machines back then), and the Arctic “Red Paint” cairn-building and such dates five or seven thousand years before Mystery Hill (hence, probably unrelated).