AND...
When using Academic Search Premier and Historical Abstracts, be sure to use "and" between the terms. (E.g. Black death and Italy)
Quotation Marks...
When using JSTOR an AND is automatically inserted between every word. To keep words together as a phrase, use quotation marks. (E.g. "Black death" Italy)
Asterisk*
An asterisk at the end of a word can find alternate endings. (E.g. Jew* will find Jew, Jews, Jewish, etc)