In the field manual they say "Finally, the very practice of simple sabotage by natives in enemy or occupied territory may make these individuals identify themse

In the field manual they say "Finally, the very practice of simple sabotage by natives in enemy or occupied territory may make these individuals identify themselves actively with the United Nations war effort..." I thought this was published before the UN was founded. Did the term "United Nations" have a different meaning during WWII? Was it a common term that latter was given to the official organization we know today?