Consider the persuasion of making a sale. That's not force. People can sell political ideas in the same way, they can spread virally.

EDIT: Also I consider economics, politics and marketing as basically "mass psychology". Hence all the problems with replication in those fields.

EDIT 2: And with these things being psychology, there's a big "default biological drives" component. A lot of the motivations for political etc actions are internal to each person.

Persuasion is the art of supplying facts to enable mutual self-interest. Not everyone has an implacable class interest.