Korean Collectivism:

우리 나라, 우리 집, 우리 형/누나/오빠/언니/동생, 우리 아버지/어머니, 우리 남편/아내

'우리' means a group including the speaker himself/herself.

  Singular Plural
1st Person 나/저 우리/저희
2nd Person 너/당신 너희(들)
3rd Person (그/그 사람/남자, 그녀/ 그 여자) (그들/그 사람들/남자들, 그 여자들)

By referring to self with the term inherently denoting plural, the speaker expresses his or her bond/in-groupness to the entity.