The words “long ago” are typically used to refer to the time of Israel’s salvation from Egypt and the covenant at Horeb. The “word” of which this verse speaks is the Torah (Genesis to Deuteronomy) that Moses gave to the people at that time. The Lord had now done exactly what he said in Leviticus 26:1–46 and Deuteronomy 28:1–68. It was only to be expected, especially after all the prophets who came to call the people back to that Horeb covenant.
See, for example, the clear warning in Deuteronomy 28:49–52: “The Lord will bring a nation against you from far away, from the end of the earth, swooping down like the eagle, a nation whose language you do not understand…. They shall besiege you in all your towns, until your high and fortified walls, in which you trusted, come down.”
17 The LORD has done what he purposed; he has carried out his word, which he commanded long ago; he has thrown down without pity; he has made the enemy rejoice over you and exalted the might of your foes.