A more thorough explanation:

The restrictive principle of sovereign immunity is a doctrine that limits the immunity of foreign nations in the United States. It states that a foreign nation's immunity does not apply to claims arising from the nation's private or commercial acts, but protects the nation only from claims arising from its public functions.

For example, if a foreign government owns a commercial business in the United States and is sued for a breach of contract, the restrictive principle of sovereign immunity would not protect them. However, if the same foreign government is sued for actions taken in their official capacity as a government, such as a decision made by their embassy, they would be protected by sovereign immunity.

The restrictive principle of sovereign immunity is recognized in international law and is codified in the Foreign Sovereign Immunities Act. It is important to note that this doctrine only applies to claims made in the courts of the United States.