联盟 means "alliance" or "league" and refers to a formal or informal union of groups working together toward a common goal. It is used in historical, political, and organizational contexts.
这几个国家组成了一个经济联盟。
zhè jǐ gè guójiā zǔchéng le yí gè jīngjì liánméng.
These several countries formed an economic alliance.
战争时期,各部落结成了联盟共同抵御外敌。
zhànzhēng shíqī, gè bùluò jiéchéng le liánméng gòngtóng dǐyù wàidí.
During wartime, the tribes formed an alliance to resist foreign enemies together.
这个联盟的成员国越来越多了。
zhège liánméng de chéngyuánguó yuè lái yuè duō le.
The member states of this alliance are increasing.