Nutiquam- I hav long ago already quit this kin of forum-because the vast majority of posters come to this with minds already made up. But I will give a very straight answer and it is :YES. In many spheres, the law of he land is based on halacha. The laws of marriage and divorce, in many towns the laws of shabbos , In all of official Israel the laws of kashrut, and many other instances. So your inference that it is not based on halacha is wrong.
But, why does this matter? There were plenty of non-religious kings in Baiys rishon and others in Bayis Sheni and yet it did not invalidate the legitimacy of Eretz Yisroel. Why should this matter now?