in star wars there are two forces,the darkside & the lightside. in the entire star wars series these are the 2 constants. however, these forces do not stay the same throughout the entire series they go through changes in the first original trilogy there is the empire which is the darkside and there is the rebellion which is the lightside. in the prequels there is the republic which is the prequels embodiment of the lightside and the sith which is their embodiment of the darkside.finally in the sequel trilogy (yes that is what it is actually called) there is the resistance which is the lightside and there is the first order which is the darkside. This is one of the few constants that remains in place in all star wars films.