2al·ly 
/əˈlaɪ/ verb
al·lies; al·lied; al·ly·ing /əˈlaɪ/ verb : to join (yourself) with another person, group, etc., in order to get or give support — often + with or to [+ obj] ▪ She's allied herself with the moderates on this issue. ▪ countries allying themselves with the EU ▪ He'll even admit that he's hoping to ally himself to a wealthy family by marriage. [no obj] ▪ They've allied with their former enemies. — see also allied
