Lamentations 4:11 (ESV)

11 The LORD gave full vent to his wrath; he poured out his hot anger, and he kindled a fire in Zion that consumed its foundations.

This verse is a humble acknowledgement that the Lord has done what is right. The Babylonians may have been the instrument he used to burn Jerusalem down with fire (2 Kings 25:8–9), but it was ultimately he who did it. This was not an uncontrolled fit of anger. God had acted on the basis of the covenant that he made with Israel, and that they themselves had confirmed (Deuteronomy 11:29–32; Deuteronomy 27:1–26; Joshua 8:30–35).

For a long time, God’s people have been breaking this covenant. During all this time, God has stored up his wrath (see Romans 2:5). But now he has finally “poured out” all of it on Jerusalem. That is why the city’s foundations have been consumed by fire.

The foundations can be understood both literally (as the buildings that were destroyed by the fire) and figuratively (as the political, economic, religious, and social foundations of society).