Michael Chui is right. The idea of ownership or claim to the land gets thrown about a lot but what you have to understand is that there is no one regulating or enforcing any of these claims. Like Michael said, he could claim possession of the land under the white house but who is going to listen to him? Is anyone going to back up his claim?
Israel took possession / made a claim on land that really belonged to the Palestinian state, but they got some powerful states to back up their claim and in doing so they became a legitimate state. Similarly, if they had done everything they did and all the powerful states had denounced them and told them that was Palestines land and they had to get off or they would be removed forcibly, what is their claim worth?
Secondly, there are plenty of stateless peoples with a very legitimate historical claim to land that are being ignored for the most part. For example,
Kashmiri people,
Kurdish people,
Sahrawi people. These are some of the more major ones but there are plenty of other examples, especially in many parts of the developing world where the people drawing the maps failed to take in to account the realities on the ground.