An occupation occurs when there are no weapon tokens in a developed settlement. Upon placing the occupation monolith, the AI will start to build AI spawners on towers around your base. If you have any manufacturing tokens the AI will set up cable relays to take your power-ups.
Steps to becoming unoccupied
Kill as many AI as possible around the settlement.
Stop the spawners from creating new AI by shooting the electric beam at their bottom.
Place a weapon token in a safe place away from spawners.