Blockades are barriers created by ships, aircraft, minefields, or other means meant to prevent an area from receiving or sending out supplies, medical materials, weapons & ammunition, trade goods, people, and/or communications. Generally, this is accomplished by encircling the area with people or vehicles intent on intercepting anyone who attempts to pass through the blockade. Blockades differ from sieges as the end goal typically in not to conquer an area, but rather to force diplomatic concessions. There may be blockade runners, which attempt to circumnavigate or evade the blockade to pass through.
Blockades may not only prevent the transfer of materials but may also prevent the transmission of communications. If this is the case, a means of intercepting or jamming signals would be required.
When designing blockades, consider why it was established, how it prevents movement across it, and how blockade runners may circumnavigate it.