Q. Some rabbis say Israel is not allowed to cede territory. How do they decide what may or may not be ceded?
A. The Torah specifies the boundaries (e.g. Gen. 15:18), but political realities always caused some fluidity. In the days of David and Solomon the borders could not have been sacrosanct since Solomon was willing to give 20 Galilee towns to Hiram of Tyre (I Kings 10).
The rabbis had many debates about what was meant by “Land of Israel” and resorted to pragmatic considerations such as the number of Jews in a particular place. Not only was there uncertainty about where Israel began and finished but there was (and is) even an issue with Jerusalem. One might have argued that the walled city defined
Jerusalem, but it wasn’t halachah that built the city wall, nor halachah that decided where the modern city should extend.
I totally agree that Jerusalem is Israel’s capital city, but where does Jerusalem begin and end? As a resident I vote in municipal elections and pay rates, but I live in a central neighbourhood. What about those who are on the periphery?