Forming an alliance is a process in which two or more parties come together to form a mutually beneficial relationship. This could be for political, economic, military, or social reasons. The term 'forms an alliance' can be used to describe the process of two or more entities joining forces to achieve a common goal. In the crossword, the solution to the clue 'Unites' (6 letters) is FORMS. Therefore, the complete phrase is FORMS AN ALLIANCE.