be equivalent / do *something on an equal basis / be equal

face each other / stand opposite to / be opposite to / face

conflict / clash / be conflicting / be opposite

join forces / team up / cooperate / work together / collaborate

attach *oneself to / feel attached to

be in contact (with the enemy) / communicate (with the enemy)

have relations / have an affair

get through to each other / communicate / understand

communicate / relate

serve / play / act