10 warp point limit

From SEWiki

In Space Empires IV and Space Empires III, no system may have an additional warp point created in it if it already has 10 or more warp points in it. This gives players the ability to prevent the opening of new warp points (by a hostile neighbour, for example) into their territory. All the player has to do is open 10 warp points of their own (preferably all from a single, heavily-fortified sector) and the possibility of a stellar manip sneak attack becomes a thing of the past. Note that in SEIV, custom maps may be created in the Map Editor with more that 10 warp points.

Since version 1.45 of SEIV, the System gravitational shield facility has made another method of warp-point denial available. Warp-point denial can be used for turtling.