Answer:
Force
Step-by-step explanation:
Newton's first law states that: "An object maintains its state of rest or motion unless acted upon by an external force"
This means that an object that is at rest will remain at rest unless an external force acts upon it and forces it to start motion. Whereas, a moving object will keep moving in its direction unless an external force acts upon it forcing it to either come to rest or change its direction of motion.
Based on the above, force is responsible for all changes in motion.
Hope this helps :)