It is an essential attribute of sovereignty that a sovereign state can acquire foreign territory and can, in case of necessity, cede a part of its territory in favour of a foreign State, and this can be done in exercise of its treaty-making power. Cession of national territory in law amounts to the transfer of sovereignty over the said territory by the owner-State in favour of another State. There can be no doubt that such cession is possible and indeed history presents several examples of such transfer of sovereignty.
It is true as Oppenheim has observed that “hardship is involved in the fact that in all cases of cession the inhabitants of the territory who remain lose their old citizenship and are handed over to a new sovereign whether they like it or not”; and he has pointed out that “it may be possible to mitigate this hardship by stipulating an option to emigrate within a certain period in favour of the inhabitants of ceded territory as means of averting the charge that the inhabitants are handed over to a new sovereign against their will” (p. 553).
But though from the human point of view great hardship is inevitably involved in cession of territory by one country to the other there can be no doubt that a sovereign state can exercise its right to cede a part of its territory to a foreign state. This power, it may be added, is of course subject to the limitations which the Constitution of the state may either expressly or by necessary implication impose in that behalf; in other words, the question as to how treaties can be made by a sovereign State in regard to a cession of national territory and how treaties when made can be implemented would be governed by the provisions in the Constitution of the country. Stated broadly the treaty-making power would have to be exercised in the manner contemplated by the Constitution and subject to the limitations imposed by it.
 (Oppenheim’s “International Law” – by Lauterpacht, Vol. I, p. 551 (8th Ed.))