What are the two key factors driving dramatic differences in galactic shapes over billions of years?

Answer

The initial spin of the material and the gravitational interactions it endures

The dramatic differences in galactic shapes are largely driven by the interplay of two factors: the initial spin of the material that formed the galaxy (angular momentum) and the gravitational interactions it endures throughout its life.

What are the two key factors driving dramatic differences in galactic shapes over billions of years?
galaxiesastronomystructureformationshape