Adam Clarke on Psalms 76:12

He shall cut off the spirit of princes - Even in the midst of their conquests, he can fill them with terror and dismay, or cut them off in their career of victory.

He is terrible to the icings of the earth - "He is the only Ruler of princes;" to him they must account. And a terrible account most of them will have to give to the great God; especially those who, instigated by the desire of dominion, have, in the lust of conquest which it generates, laid countries waste by fire and sword, making widows and orphans without number, and extending the empire of desolation and death.

Thus all are under his dominion, and are accountable to him. Even those whom man cannot bring to justice, God will; and to judge them is one grand use of a final judgment day.