Like with Manifest Destiny the problem comes when the area you want to decide to call your own already has people living there. I'd also add that there is no sort of human right to having your own homogeneous country. Most countries in the world have large sects of the population that would like to form their own autonomous states, many with populations substantially larger than that which initially carved out Israel for themselves. Unfortunately we live on a planet in which most of all land that's remotely habitable has been claimed by somebody.