The source

I am not the user you where interacting with, but these ideas can be found in Carl Schmitt in his work The Nomos of the Earth in the International Law of the Jus Publicum Europaeum.

This is because The Nomos of the Earth provides his most comprehensive exploration of how sovereign authority and geographic space are legally and historically intertwined. The previous comments are about authority's spatial claim, and this book is precisely where Schmitt develops that idea at length.

An important fact to know about Carl Schmitt follows:

In 1933, Schmitt joined the Nazi Party and used his legal and political theories to provide ideological justification for the regime. He held various positions on Nazi councils, including the Prussian State Council and the Academy for German Law, and served as president of the National Socialist Association of Legal Professionals.

https://en.wikipedia.org/wiki/Carl_Schmitt

A counterpoint

Perhaps the most pointed philosophical counterpoint to the text's use of "roots" comes from the work of Gilles Deleuze and Félix Guattari, which was later applied to national identity by the philosopher Édouard Glissant. His seminal work Poetics of Relation has been used by scholars across the world to understand the rapid transformation of a multicultural world.

They critique the root as a metaphor for a singular, vertical, and exclusionary origin. Glissant argues that nations shouldn't speak of having "roots," as this implies one unique ancestral heritage.

Instead, he champions the image of the rhizome (a plant with a network of interconnected, horizontal roots) because it better captures a multicultural reality where identity is not fixed but is a dynamic, relational, and non-hierarchical network.

Where the text's concept of "roots" traces a lineage back to a point of origin, the rhizome celebrates the connections made in the present.