We may never give away land of Eretz Yisroel, and even land surrounding Eretz Yisroel that might harm the security of Eretz Yisroel.
The Rebbe frequently invoked the following halachah of Shulchan Aruch when speaking about the obligation to maintain control over Yehudah, Shomron, and other parts of Eretz Yisrael, as well as the land surrounding Eretz Yisroel. Giving up control of these areas makes it easier for the enemies of the Jewish people to conquer the entire land.
שולחן ערוך אדמו"ר הזקן סימן שכ"ט הלכה וא"ו:
נָכְרִים שֶׁצָּרוּ עַל עֲיָרוֹת יִשְׂרָאֵל, אִם בָּאוּ עַל עִסְקֵי מָמוֹן – אֵין מְחַלְּלִין עֲלֵיהֶם אֶת הַשַּׁבָּת. וְאִם בָּאוּ עַל עִסְקֵי נְפָשׁוֹת, וַאֲפִלּוּ בָּאוּ סְתָם וְיֵשׁ לָחוּשׁ שֶׁמָּא בָּאוּ עַל עִסְקֵי נְפָשׁוֹת, וַאֲפִלּוּ עֲדַיִן לֹא בָאוּ אֶלָּא מְמַשְׁמְשִׁים לָבֹא – יוֹצְאִים עֲלֵיהֶם בִּכְלֵי זַיִן וּמְחַלְּלִין עֲלֵיהֶם אֶת הַשַּׁבָּת. וּבְעִיר הַסְּמוּכָה לַסְּפָר, אֲפִלּוּ אֵינָן רוֹצִים לָבֹא אֶלָּא עַל עִסְקֵי תֶּבֶן וְקַשׁ – מְחַלְּלִין עֲלֵיהֶם אֶת הַשַּׁבָּת, שֶׁמָּא יִלְכְּדוּ הָעִיר וּמִשָּׁם תְּהֵא הָאָרֶץ נוֹחָה לִכָּבֵשׁ לִפְנֵיהֶם:
[The following laws apply] when non-Jews take up arms against Jewish towns: If [the non-Jews] come [to attack the towns] for financial gain, the Shabbos may not be desecrated because of them. If, however, [the non-Jews] come to kill, and even if they come with no expressed intent, but there is concern that perhaps they come to kill, one should confront [the non-Jews] while armed and desecrate the Shabbos because of them. [Indeed, these steps may be taken] not only when their arrival is imminent, but even if [the non-Jews] are merely threatening to come. In a town that is near the border, even if [the non-Jews] only seek to come for matters concerning hay and straw, the Shabbos may be desecrated because of them, lest they capture the town, and from there, the [entire] land will be easier for them to conquer.
-Excerpt from SIE
In the sichah linked below, the Rebbe discusses how a Jew must remember that he does not belong in golus. Knowing this helps strengthen our resolve not to give away the land Hashem has given us. The Rebbe speaks in clear terms about the danger, halachically and also practically, of giving away even a small parcel of land.