| It doesn't stop|
at the water's edge
"Grassroots" is a term often used to refer to movements (usually social or political) that have been created as a natural response to some perceived social or political wrong or cause.
These organizations (at least those that are genuine in origin) tend to be locally based as opposed to national in terms of scale, their backing tends to rest entirely on ordinary people as opposed to a formal organization, and their funding, if any, comes from voluntary donors within the movement or from their sympathizers.
By contrast, the faked version of this would be Astroturfing (so named after the artificial grass product), where a corporation or some other formal party with a direct interest in whatever the issue at hand is (such as a product like the health risks of cigarettes or a political cause like nativism) either covertly and artificially creates a "grassroots" organization (which is in reality a shill for their interests), or they will co-opt a genuine grassroots movement for their own purposes.