What causes motion?
If anything is acting on a partilce, it will keep moving along a straight line, with constant velocity (in all the inertial reference frames). In this sense, nothing causes the motion.
A change in this kind of motion, that is, an acceleration or a curve in the trajectory, is caused by a force, according to the Newton equation F = dp/dt. "Nowadays" we prefer to avoid the concept of force F, using instead the idea of field, which is independet from the particle and from its parameters (mass, charge, ... ): you can say that the field permeate the space, whether the particle is there or not.
The kind of motion that causes objects to move in a circle is formed or produced when the object is suspended from another object that is stationary. And because the moving object is suspended it will be subject to gravity which will cause it to move in a circle or circular-like motion. The actual kind or cause of the motion is a simple swaying or arc-like motion.