What does Psalm 18:45 mean?

Scripture records that David's military success was intimidating to foreign nations. According to this verse, military powers who had been aggressive towards Israel surrendered to David in fear and trembling. They lost their courage. Their fortresses did not provide security against David. Some, rather than attempting to fight a losing battle, voluntarily made peace with Israel—one example being Toi, king of Hamath (2 Samuel 8:9–10). Despite this reputation, David didn't use this advantage to expand beyond the borders of Israel. He subdued those who had attacked God's people, turning them from hostility to deference.

Ungodly men may feel secure in their wealth, political power, or military strength, but someday the Lord will judge them, and they will tremble before Him. Revelation 6:12–17 describes what happens when the sixth seal judgment begins in the tribulation period. A great earthquake, a solar eclipse, and a meteorite shower occur, and "the kings of the earth and the great ones and the generals and the rich and the powerful, and everyone, slave and free, hid themselves in the caves and among the rocks of the mountains." They call upon the rocks to fall on them and hide them from the one who is seated on the throne and from the wrath of the Lamb. They recognize that great day of wrath has arrived, and no one can withstand it.

All the strength of all the nations is as nothing compared with the power of the King of kings and Lord of lords!