Or conflict studies for that matter? Good Question.
I would argue that when we periodisize the temporal domain of our theories we are essentially including another variable in our models. This is because periodization is always done on the basis of some variable and the values it takes. Thus a lot of the concerns that come with including variables in a model also apply to including periods. First of all one must choose which variable out off many possible is going to be the criterion on which periods will be demarcated. The choice of demarcation is crucial for not all possible demarcations are mutually inclusive or mutually exclusive. The first case, of mutually inclusive demarcations, can create ambiguity of results, while the second, of mutual exclusive demarcations, can lead to the muting of the effect of some important variable X that our demarcation variable leaves out.