Contemptuous/mocking smile, remark or tone, which connotes malicious cruelty and heartless. It's like he is mocking his subjects, and hows his insolence and contempt for subjects that he views as below him. This presents the King's arrogance, confidence and sense of superiority. This is reflective of Shelley's own anti-violence stance, as he was against all military exploits and thus also against the "cold commands" that initiate them.