sorry a bit late but you can use ILSpy to dissect the code which is in Assembly-CSSharp.dll in which in references we can find all the scripts. the necessary code I found was that it picks a random number between 1 and 15 every time you draw. If its lands 1 - 3 its large expand, 4 - 6 medium expand, 7 - 9 small expand. 10 new nations, 11 split, 12 small split, 13 union and 14 is new leader
edit: this is outdated now