If you are new to these topics, the Select Bibliographies at the end of the relevant entry in the Max Planck Encyclopedias would be a useful starting point:
Subject terms to use in subject searches on SOLO:
Intervention (international law)
Responsibility to protect (international law)
Humanitarian intervention
Humanitarian assistance
Atrocities - prevention
Crimes against humanity - prevention
Genocide intervention
Conflict management
Security, International
Pay attention to the Location of the results of SOLO searches.
Sometimes Bodleian Reading Rooms other than the Law Library will have materials to support your studies. The first book is an example where the Bodleian Social Science Library has a print copy, should you prefer that to reading the ebook.
Humanitarian Intervention and the Responsibility to Protect by Most of the texts on these topics in the Law Library will have shelf marks beginning Internat. Internat shelf marks are on Level 3,one floor above the entry level to the Law Library. It is accessible via both stairs and a pulic lift. There are reader spaces and a PCAS machine on Level 3, but readers are also welcome to take books from Level 3 to other floors within the Law Library if they prefer.
Note The Internat collection on Level 3 is divided into broad subject areas. You may find that your SOLO results are taking you to different, separate sections- not necessarily adjacent to each other.
Humanitarian Intervention : a history by 
Humanitarian Intervention by 
Responsibility to Protect by 
The Responsibility to Prevent: overcoming the challenges of atrocity prevention by