@neologist,
I was referring to a Talmudic comment, which I had read in some book was a reflection on an actual oath taken by exiled Jews in Babylon after the destruction of the second temple. That book is not with me anymore so I can't look up the reference for the historical oath to a Babylon king. I can't find it online either, which makes me doubt about the certainty of that historical interpretation...
The Talmudic passage is described here:
http://en.wikipedia.org/wiki/Three_Oaths
You can read the full tractate on the Jewish Virtual Library (Ketubot 110b and 111a) but most of it is about how much money to pay a divorced wife.
In essence, the 3 oaths say that the promised land is still somewhat promised but men should not do anything to secure the promise, e.g. they should not emigrate as a group or as an army to Palestine. God will care for that promised land stuff when and how he sees fit. Similarly, God will send a messiah in due time, but men should not fret about it and name this or that guy messiah (as some rabbis did in 130 with Simon Bar Kokhba).
This was useful I guess because the Jews didn't need yet another messianic war, after losing two or three in a row. The rabbis had to cool off messianic passions. In effect they say: forget about messianism and national liberation. God will take care of that.
The three oaths are nowadays the main basis for some orthodox Jews' opposition to Zionism. But the trick is: the third oath was that God was to see to it that the nations among which the Jews are exiled don't treat them too bad. Some say that side of the bargain was broken during the Holocaust, giving Jews a new right to come en masse to Palestine.