Deuteronomy 4:30 (ESV)

30 When you are in tribulation, and all these things come upon you in the latter days, you will return to the LORD your God and obey his voice.

The primary application here is to tribulation in Israel's immediate future. And Israel would indeed experience trial in the days of the Judges, the period following the first part of the conquest. But the tribulation of this verse would be even more apparent in the fall of the two kingdoms and the exile from the Promised Land. Such misery will be enough to prompt them to return to God.