In the last century of the 3rd millennium BC, it is believed that the kings of Ur waged several conflicts around the frontiers of the kingdom. These conflicts are believed to have been influenced by the king of Akkad. As we have little evidence of how the kings organized their forces, it is unclear whether defensive forces were in the center or outside the kingdom. One of the things we do know is that the second ruler of the dynasty, Šulgi achieved some expansion and conquest. These were continued by his three successors but their conquests are less frequent with time.