The first step, of course, is to determine the most significant political and cultural changes that strike you as the compelling factors in the change you identify--which means you also have to identify the primary change. For example, consider change over time in America between 1940, 1950 and 1960.
In 1940, big bands were in the swing of power and government was escalting social programs. In 1950, music had changed to early rock and roll and government was battling through McCarthyism. In 1960, the children of WWII veterans rebelled against newly won consumerism and listened to psychedelic rock and roll while Vietnam heated up before coming to a boil (i.e., worsened until reaching a decisive level).
A thesis for this would be drawn from identifying cultural change as moving from conservatism and post-war economic expansion to rebellion and naturalism while political change moved from global war to suspicion to local engagements.