When the Germans occupied Belgium, Herge decided to stop the story in mid-adventure
It's also worth noting that in this first, uncomplete version, Tintin never met the emir Ben Kalish Ezab. Also, the Thompsons crashed into the mosque BEFORE Tintin encountered Muller in the desert, which means that they (the Thompsons) weren't at hand to save Tintin. And finally, Tintin hadn't even met Haddock yet! All in all, this means that the story would have developed in another direction if it was completed in 1939.
After the war, Herge founded the weekly "Tintin magazine" and a second, completed, version of "Black Gold" was published, again set in the British Mandate of Palestine. In this version, as far as the first half was concerned, Herge used the same drawings as he did in the pre-war version but they were smaller and in colour ("Le Petit Vingtieme" version had been in B&W and much larger). When the book version was published soon afterwards, Herge redrew the first half completely in order to include a scene where Tintin talks to Haddock over the phone and a sub-plot in which everyone fears an imminent war.
Well, Hergé didn't redraw the first half completely to include the phone call with Haddock, he just replaced some panels on page 3 and re-arranged the same page. He did redraw page 1, though, and he also shortened the story a bit on pages 23 and 24 (which appeared on three pages in the Tintin-magazine and included a cut scene where Tintin drinks from an oil-infested well).
By the time the book was due to be published in English in 1972, the state of Israel had long been up and running, thus the scenes in the British Mandate of Palestine - with British troops, Jewish Zionists and Arab fighters - were somewhat dated. The British publishers insisted on an update and Herge therefore redrew a dozen or so pages in order to reset the action to the fictional kingdom of Khemed.
Yes, it was at this time that Hergé (and Bob de Moor) completely redrew and/or re-arranged pages 7-20. And Khemed was of course originally invented for Red Sea Sharks
, even if that story takes place after Land of Black Gold.