(b) Conditions of Existence. A blockade presupposes,—
- 1. A state of war.
- 2. Declaration by the proper authority.
- 3. Notification of neutral states and their subjects.
- 4. Effective maintenance.
(c) Blockade a War Measure. The so-called pacific blockade differs in its purpose and method to such an extent as to cause many to deny it any standing in international law. Only a belligerent can institute a blockade which other states are bound to respect, as, without war, there are no neutrals. The blockade may continue even until the conclusion of peace. The agreement to a truce or an armistice does not put an end to the blockade.
(d) Declaration. Blockade can be declared only by the proper authority.
As war is a state act, only the person or authority designated by the constitution or law of the state can declare a blockade. Such a declaration must, in general, come from the chief of the state. In certain cases a blockade declared by an officer in command of forces remote from the central government is held to be valid from the time of its proclamation, if the act of the commander receives subsequent ratification from the central authority.
(e) Notification. Neutrals must be notified of the existence of a blockade. This notification may be:—
- 1. By official proclamation announcing the place to be blockaded, and the time when the proclamation becomes effective.
- 2. By notification to vessels when they come near the place blockaded.
- 3. The use of both the above methods.
The theory of the American and English authorities has been to assume a knowledge of the blockade on the part of subjects if the political authority of their state had been informed of the existence of the blockade before the neutral vessel left port. In practice both powers have in recent years given a neutral vessel warning of the existence of blockade of a port before seizure.[470]
The French rule is to give in every instance an approaching neutral vessel warning of the existence of a blockade, and to consider the notification to the neutral state authorities as merely a diplomatic courtesy.