Sovereignty is involved only when political acts are accomplished by the state. . . . However, the state is not bound to confine itself to a political role, and can . . . buy, own, contract, become creditor or debtor, [become criminally liable], and engage in commerce. . . . In the discharge of these functions, the state is not acting as public power, but does what private persons do, and as such, is acting in a civil and private capacity.
Id. at iiiii.
The text of the Constitution does not require the act of state doctrine; it does not irrevocably remove from the judiciary the capacity to review the validity of foreign acts of state. . . . [The doctrines] constitutional underpinnings . . . [arise] out of the basic relationship between branches of government in a system of separation of powers.
Banco Nacional de Cuba v. Sabbatino, 376 U.S. 398, 423 (1964).