From the book "Sapiens":
One reason German soldiers and civilians thought not all was lost was that they believed German scientists were about to turn the tide...
From the above sentence there were two 'was ' It is hard to find the subject of the first was . If all is the subject , all I think should need plural verb . Please let me know it .
To add to oerkelens's answer: "One reason" is the subject of the second "was". If you delete "German soldiers and civilians thought not all was lost", it explains the second "was". I'm reading Sapiens, too!
The second was is concerned with the "One reason of German soldiers and civilians". And the first one points to "all" in this case "all" is used as collective noun.
