400. That’s an error.

Google cannot redirect you to http://www.amazon.com/exec/obidos/external-search/?field-keywords=Esquisses+historiques+des+principaux+%C3%A9v%C3%A8nemens+R%C3%A9volution+fran%C3%A7aise...&index=books because the request was invalid.

This might be because the link was created a long time ago. Try your search again on Google. That’s all we know.