It seems the Bone live in a feudal-monarch society. By becoming emperor, one must kill or exile the current ruler and take the throne as according to a popular rhyme on Bone, "Ya snag the throne, ya rule on Bone/He who dies is food for the flies" where as Pelvis always plots to kill Femur for the throne and fails. The Bone warriors have a sense of honor and if they were to retreat under orders of the Emperor such as Femur they would find it against their code and be seen as cowards to others, thus plotting schemes to assassinate the emperor unless something is done to correct the mistake.