Perhaps you should try some spelling variations:
"industrial concentration camp" » "industrial collaboration camp", "industrial organization camp", "industrial location camp", "industrial concentration camps"
"initial concentration camp" » "spatial concentration camp", "initial configuration camp", "metal concentration camp", "initial concentration camps"

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"initial concentration camp\") OR (\"industrial concentration camp\"))".
• Removing quotes may allow a broader search: (( initial concentration camp ) OR ( industrial concentration camp )).
• Adding a wildcard symbol may retrieve word variants: (("initial concentration camp") OR ("industrial concentration camp"))*.