“I was under the impression that halacha recognizes conquest as creating ownership. The British conquered Palestine from the Ottoman’s it was theirs not the inhabitant’s and certainly not the neighbors”
The Balfour Declaration was made by the British when the Ottoman Empire still controlled Eretz Yisroel. The British did NOT control the land at the time. By time the British later gained control of the land, they did not espouse or support the principles of Balfour.
So you have another reason it is halachicly inapplicable.