Perhaps you should try some spelling variations:
immigration policies » immigration policy, migration policy
integration theories » integration theorems, integrationstheorie 2, integration theory
mass immigration » mass migration, _ immigration
supply mass » supply case, supply main, supply many
supply grid » supply crowd, supply great, support grid

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( supply mass immigration policies. ) or ( supply grid integration theories. ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( supply mass immigration policies. ) OR ( supply grid integration theories. )).
• Adding a wildcard symbol may retrieve word variants: (( supply mass immigration policies. ) or ( supply grid integration theories. ))*.