Carol, you asked "Keith, I want to see the language that defines who can blockade whom. The language I've seen so far says that a country can prevent foreign countries from bringing anything to the shores of the country that is enforcing the blockade. I have not yet seen any other definitions of who can conduct blockades and who can be blockaded."

A blockade is a method of warfare between belligerent states.
Here are the relevant San Remo sections.

Blockade

93. A blockade shall be declared and notified to all belligerents and neutral States.

94. The declaration shall specify the commencement, duration, location, and extent of the blockade and the period within which vessels of neutral States may leave the blockaded coastline.

95. A blockade must be effective. The question whether a blockade is effective is a question of fact.

96. The force maintaining the blockade may be stationed at a distance determined by military requirements.

97. A blockade may be enforced and maintained by a combination of legitimate methods and means of warfare provided this combination does not result in acts inconsistent with the rules set out in this document.

98. Merchant vessels believed on reasonable grounds to be breaching a blockade may be captured. Merchant vessels which, after prior warning, clearly resist capture may be attacked.

99. A blockade must not bar access to the ports and coasts of neutral States.

100. A blockade must be applied impartially to the vessels of all States.