The claim is based, Richard, on that UN resolution of 1947. The state of Israel was recognised on the day of its proclamation by both the US & the Soviet Union: either of whom along with the UK, could have vetoed the resolution in the Security Council; US & the Soviets both voted in favour, however, & the UK, on the plea that as mandatees they might have been perceived as an interested party, chose to abstain.

It was in accordance with that resolution that the state was proclaimed & recognised. The authority of the League of Nations, as you say above, might have been suspect; but I don't see how you can dispute the legal right of the UN to pass the resolution that brought Israel, now for many years a member of the UN, into legal being: a right and legality disputed by no nation other than those belonging to the Arab/Islamist confederacy ~~~

~~~ Which seems to me to be the response to your ~ I suspect perverse, tendentious and intentionally provocative ~ enquiry which seems to me based on exceptionally dubious and probably racist grounds,as to the legal legitimacy of the existence of the state of Israel at the eastern end of the Med.

~M~