Perhaps you should try some spelling variations:
"immigrants agricultural laborers mexico." » "migrant agricultural laborers mexico.", "immigrants cultural laborers mexico.", "immigrants agricultural labor mexico."
"immigrants agricultural class mexico." » "migrant agricultural class mexico.", "immigrants cultural class mexico.", "immigrants agricultural laws mexico.", "immigrants agricultural law mexico.", "immigrants agricultura caso mexico.", "immigrants agricultural press mexico."

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("immigrants agricultural laborers mexico.") or ("immigrants agricultural class mexico."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("immigrants agricultural laborers mexico.") OR ("immigrants agricultural class mexico.")).
• Removing quotes may allow a broader search: (( immigrants agricultural laborers mexico. ) or ( immigrants agricultural class mexico. )).
• Adding a wildcard symbol may retrieve word variants: (("immigrants agricultural laborers mexico.") or ("immigrants agricultural class mexico."))*.