Stability manager (level) is a parameter that can be set inside the Setup tool.
This parameter was introduced to improve the game stability performances.
Each level has a remark aside, i.e.: 3 (average PCs).
Technically speaking, it's a sort of delay performed during the game updates - all engine core inner procedures performed to refresh all game items such as nations, armies, etc. etc. (which are frequent, being GI a real-time game!). This sort of delay is useful in order to prevent "collisions" in data-accesses-and-modifications that could be caused in a multi-threaded application...
Well, very complex explanation? In simple words, let's say higher values introduce a bit slowness factor in game performances. Use level 3, it should be ok...
