Reavers, Draconians, and the Forsaken Armada vie for "control" of each sector. Reavers are able to 'occupy' Forsaken controlled sectors once the Draconian Military presence has been removed from power. If the Reavers occupation is in effect, this will increase the Uranium payout for all Dredge Fleets in that sector.
Other iterations of this feature may be introduced in the future.
Sector Influence can be accessed by clicking the Sector indicator at the top-middle of the World Map.
If you hover over the Sector Influence indicator at the top of the screen, a popover will appear showing who currently controls the Sector:
Once the Sector Influence tab is clicked, the Sector Influence window will appear:
Note how the above image shows an Alliance currently controls this sector meaning the Reavers have increased their mining efforts. The "Reaver occupation" indicates that Dredge fleets now contain more Uranium than normal.
As the Overview states, Alliances gain Influence by earning Alliance Points. The Draconians gain Sector Influence over time.
Players can reduce the influence of the Draconians in a sector by destroying Draconian bases.
Hitting Targets In Other Sectors
Hitting targets outside of your own sector will have slightly different outcomes in regards to Sector Influence. If you are hitting a target for alliance points (another player's base or a salvage) it will contribute to your Alliance's Influence in your home sector, but not the sector you are hitting the targets in. On the other side, Destroying a Drac Base will decrease the Draconian Influence in the sector you are hitting, but not your home sector.