1)
When will Hashem gather them from all lands?
1.
Radak (36): It is after the 70 years of Galus Bavel 1 .
1
From which other lands will they return? Radak (31:14) said that the 10 tribes did not return from Galus Bavel! From Bavel, the Jews scattered "b'Chol Medinos Malchusecha" (Esther 3:8); Achashverosh ruled over the entire world (Megilah 11a). (PF)
2)
Due to what Midah will Hashem gather them?
1.
Rashi: With mercy, He will gather them from where he cast them off amidst anger.
2.
Malbim: From the beginning, I cast them away in order to fix them and return them.