alliance n.

c. 1300, "bond of marriage" (between ruling houses or noble families), from Old French aliance (12c., Modern French alliance) "alliance, bond; marriage, union," from aliier (Modern French allier) "combine, unite" (see ally (v.)).

The general sense of "combination for a common object" is from mid-14c., as are those of "bond or treaty between rulers or nations, contracted by treaty" and "aggregate of persons allied." Unlike its synonyms, "rarely used of a combination for evil" [Century Dictionary]. Meaning "state of being allied or connected" is from 1670s. The Latin word was alligantia.