Two legal bodies in the UN

It was said in BPP that there are two legal bodies in the UN that are involve in drafting the international (The UNCITRAL and The International law commission),
My question is was there any organization that drafted the international law before the formation of this two? Since UN was formed 1945 with some core purposes ,but before then, other international organization such ICC(1919) & UNIDROIT (1926) were the only organization that were in existence. Rome convention and New York convention were not in existence until 1980 and 1958 respectively.

So who were the drafter of international law before UN core legal bodies?

Also, The international law commission was silient in BPP text book without informing us the reader the purpose and function of that organization . Could you pls summarize the function of the International law commission since only the UNITRAL was well expelained in BPP As it is only relevant in the field of international trade laws.

Thank you in anticipation.