"The situation in which a country or place is surrounded by soldiers or ships to stop people or goods from going in or out." (CD)
See also: https://dictionary.cambridge.org/us/dictionary/english/blockade?q=Blockade
The graph displays the other subjects mentioned on the same pages as the subject "Military Events--Blockade". If the same subject occurs on a page with "Military Events--Blockade" more than once, it appears closer to "Military Events--Blockade" on the graph, and is colored in a darker shade. The closer a subject is to the center, the more "related" the subjects are.