What do you mean by terrorism? Fear has always been used to achieve goals, so it's at best a vague statement.

I can offer a layman's perspective on two subjects I know a little about - terrorist violence in relation to certain American social movements. Of course this all depends on how you define terrorism, and also how you define political change.

The first thing that comes to mind is the Ku Klux Klan, who used terrorism to great effect against Reconstruction efforts in Southern states following the civil war. The initial flourishing of Black political and social life under reconstruction was halted by a decade of KKK and related White Supremacist violence against Black communities and their White allies. This led directly to the Jim Crow laws that governed race relations in the South until the mid-20th century.

At around the same time period you saw a rise in political violence coming from the other side of the political spectrum - the early American labor movement - as described in the book Dynamite: The Story of Class Violence in America by Louis Adamic. Adamic describes how violence - or more typically, the implied threat of violence - was commonly deployed by workers during labor disputes. Basically the strategy was to make owners consider between two options: consent to worker's demands, or risk seeing their factory/mine/home be blown up by dynamite. This was extremely effective in certain individual disputes, and the threat of increasing labor militancy formed the backdrop that led to important political and economic reforms, like the 8-hour work day.