God refers to both kingdoms here—the descendants of the northern kingdom of Israel as well as the southern kingdom of Judah. The return of Israel will be the larger migration because, aside from the 70-year captivity in Babylon, some of the descendants of Judah have always resided in the Promised Land. Today, the State of Israel is predominately made up of the descendants of Judah.
However, neither Israel nor Judah has truly possessed the land since the time of their respective captivities. Despite some of Judah having returned to the land, ever since the Babylonian captivity, she has only rarely and intermittently held sovereignty over it.
After Judah was taken into captivity, Babylon ruled the Promised Land under Nebuchadnezzar. Babylon later fell to the Medo-Persian Empire, which then became sovereign over Jerusalem and the Promised Land. Because of their vassal status, the Jewish captives that returned from Babylon had to ask permission from Cyrus and Darius, the Persian kings, to rebuild the wall and the Temple. The Jews enjoyed a measure of peace, but their freedom depended on the favor of the ruling Persian emperor.
After Alexander the Great conquered Medo-Persia, the Greeks became the new overseers of the Land of Promise. Jews under the Maccabees gained a measure of independence until Rome took control of the area. Thus, during the time of Christ, Jews lived in the land and even worshipped in the Second Temple, but they did not really possess the land because it was under Roman jurisdiction. Since the collapse of the Roman Empire, notwithstanding some temporary Crusader holdings, the Promised Land has been under the sway of various Arab and Muslim nations—notably the Ottoman Empire—down to modern times.
Even now, the state of Israel does not control all of the land. Jerusalem is a divided city, and the Israelis have not dared claim all of the Temple Mount for themselves, because they know that it would result in an all-out war with the Muslims. Even though the Jews regained a considerable amount of land when it declared statehood in 1948, gaining even more during the Six Day War, the ownership is endlessly argued. Judah is not truly sovereign yet. It does not yet "possess" the land in the fullest sense of the word.
David C. Grabbe
The Second Exodus (Part One)