Unlike balanced forces, we say unbalanced forces when two forces acting on an object are not equal in size.
Unbalanced forces causes can cause:
a still object to move
a moving object to speed up or slow down
a moving object to stop
a moving object to change direction
Unbalanced forces make the wagon in the diagram speed up.
Notice that because there is a bigger force and a smaller force involved, the direction of the wagon will be determined by the bigger force. The wagon is moving as a result of unbalanced forces.