There is every excuse. The Palestinians were offered most of the land (about 50X as much as they have now) in 1947 and the UN and Israel all agreed to it establishing officially recognizable permanent states but the Palestinians refused the offer leaving all of the land open to reclamation. You can't steal something from someone who doesn't own it in the first place.
King Abdullah bin Al-Hussein (1882-1951)
www.kinghussein.gov.jo