Didn the United Nations, the successor organization of the League of Nations overturn the Mandate?
No. The United Nations never overturned the Mandate. You may hear propaganda that claims otherwise, but the Mandate itself was fulfilled and expired as of midnight, May 14/15, 1948. What allowed the Mandate to expire was the establishment of the Jewish State and the British receiving the UN’s authority to turn over its authority in Palestine. The rights of the Mandate are still law. Though the Mandate itself ended, the UN never canceled nor has the authority to cancel the mandated rights.