The idea that jews would return to palestine has been a part of jewish culture since the unsuccessful rebellion against the empire.

The correct answer is - Roman Empire.

The Jews have been taken out forcefully out of their homeland on multiple occasions, by different empires. The Roman Empire was the last one to move the Jews out of Palestine, and that was the time when the Jews put on themselves the idea and hope that one day they will return to their homeland.

The reason why the Jews were moved away from Palestine on numerous occasions is because they were not willing to be under the occupation of other people and constantly rebelled. That was not seen fondly by the empires that conquered them, so they were moving them out of that territory.

After the WW II ended, the Jews did managed to get back to Palestine and form a county there, bearing the name of Israel.