The Talmud and Foreign Policy
On Sanhedrin 17b there is a discussion about the עיר הנידחת (“an idolatrous city”) that was to be destroyed. The Talmud addresses how many cities can be destroyed within a specific time period and geographic area. One of the reasons given for limiting the number of cities was to minimize the desolation of the Land of Israel. When discussing the destruction of idolatrous cities in the border areas, the reason given is how the actions of a Jewish governing authority might influence the actions of foreign powers.
תניא כוותיה דרבי יוחנן: אין עושין שלש עיירות מנודחות בארץ ישראל, אבל עושין אותם שתים, כגון אחת ביהודה ואחת בגליל. אבל שתים ביהודה ושתים בגליל – אין עושין. וסמוכה לספר – אפילו אחת אין עושין. מאי טעמא – שמא ישמעו גוים ויבואו ויחריבו את ארץ ישראל.
They do not declare three towns to be apostate towns in the Land of Israel, so as not to wipe out [Israelite] settlement in the Land of Israel. But they declare one or two (to be apostate cities]. R. Simeon says, “Even two they may not declare, but they may declare one town in Judah and one town in Galilee [to be apostate towns].” And near the frontier they may not declare even one town to be an apostate town so that gentiles will not come and destroy the Land of Israel. (This is from trans. Neusner, but I made a few slight changes, one based on MSS.)
Here are two possible explanations of the bolded clause: 1. The destruction of a Jewish town will further weaken the Jewish control over the area; 2. The destruction of a Jewish town will serve as an example for Gentiles, i.e. if the Jews are doing it, why can’t we.