The doctrine of the immunity of foreign governments from the adjudicatory and enforcement jurisdiction of national courts is rooted in two bases of international law, the notion of sovereignty and the notion of the equality of sovereigns. There is no need to rehearse the historical growth of these foundations of the modern international community. Suffice it to say that E.D. Dickinson's celebrated study, The Equality of States in International Law, furnishes a detailed account of the evolution of these notions.
Although historically the recognition of the jurisdictional immunities of foreign states may have been intertwined with the recognition of the immunity of foreign sovereigns as rulers and of the immunity of foreign ambassadors as their representatives, its juridical foundation rests on the principals of sovereignty, independence, equality and dignity of states and, additionally, on the ideas of reciprocity, comity among nations and avoidance of unilateral action in international affairs. Couched in the telling maxim, "Par in Parem imperium non habet," the principle of sovereign immunity is recognized in the jurisprudence of most nations.
Stefan A. Riesenfeld,
Sovereign Immunity in Perspective,
19 Vanderbilt Law Review
Available at: https://scholarship.law.vanderbilt.edu/vjtl/vol19/iss1/1