How we change what others think, feel, believe and do
Social Identity Theory
When we belong to a group, we are likely to derive our sense of identity, at least in part, from that group. We also enhance the sense of identity by making comparisons with out-groups.
Social identity is different from personal identity, which is derived from personal characteristics and individual relationships.
Breakwell (1978) studied teenage soccer fans, some of whom went to most games, whilst others did not go to games. Those who did not go to games were the most vehement about their loyalty and showed most in-group bias, presumably as they had a greater need to prove themselves as fans.
When abroad, especially in countries which have particularly different languages and cultures, we feel our nationality far more keenly than when we are at home. We will tend to band together in national groups, perhaps making comments about the strangeness of the natives.
Invite the other person into a group which has characteristics that you want the other person to adopt.
By all means build a social identity. Just pick the groups you join with care.