In the century after the 1648 Treaty of Westphalia, the European state system was established on the basis of the political principle of territoriality and of the legal principle of sovereign equality. The former notion entailed the effective control by the major princes within established territorial limits and the second concept established the norm of complete political jurisdiction by the prince and his government within these territorial boundaries unencumbered by any earthly, external authority.
Wood, Robert S.
"Intervention and Détente in American Foreign Policy,"
Naval War College Review: Vol. 30
, Article 5.
Available at: https://digital-commons.usnwc.edu/nwc-review/vol30/iss1/5