secede

1. V-I If a region or group secedes from the country or larger group to which it belongs, it formally becomes a separate country or stops being a member of the larger group. (从国家或大集团中正式)脱离

Singapore seceded from the Federation of Malaysia and became an independent sovereign state. 新加坡脱离马来西亚联邦成为一个独立的主权国家。

Ukraine decided to secede. 乌克兰决定独立出来。