ra_s.t.ra, nation

Ra_s.t.ra = denotes 'kingdom' or 'royal territory' respectively, in
R.gveda and later (RV 4.42.1; 7.34.11; 84.2; 10.109.3; 124.4; AV
10.3.12; 12.1.8; 13.1.35; VS 9.23; 20.8; TS 1.6.10.3; 3.5.7.3;
5.7.4.4; TBr. 1.2.1.13; MS 3.3.7; 7.4; .6; 4.6.3) [Vedic Index, II,
p. 213].

ra_s.t.ra gopa = protector of the realm (Ait. Br. 8.25),an epithet
applied to the Purohita whose function was to preserve the king and
the realm from harm by his yajn~a.

Are there PIE or IE cognates? rex?

Isn't it appropriate to note that the concept of the territorial
imperative, realm, territory as a national entity had its roots in
the days of the R.gveda? As a corollary, isn't it appropriate to
state that 'nation' as a concept is not a creation of the 17th
century Europe but had its roots in pre-history?