A rebel faction has split away from the main group.

一帮反叛者从核心组织中分裂了出去。

《牛津词典》

At the same time,they agreed to make the G20 the main group the "premier forum" to guide international economic cooperation.

VOA: special.2009.10.02

If there's a group, responsibility to help decreases and this is captured in different ways but the main idea is we all think someone else will help so we don't. There's a diffusion.

如果是一群人，帮助的责任就会分散变小,这体现在多个方面,但最主要的想法就是我们都认为别人会帮助,所以我们就不帮助了，责任被分散了。

耶鲁公开课 - 心理学导论课程节选

The leaders agreed to make the G20 the main group for their international economic cooperation, instead of the G8.

VOA: special.2009.09.26

On the other hand, the main group of people who are seeking marriages are born in the 1980s.

BBC: Q&A: Chinese dating consultant Zhou Xiaopeng

Financial advisors are the next main group of investment intermediaries, subject to even less transparency than money managers.

FORBES: Money Managers And Advisors Should Eat Their Own Cooking

The main group was the AUC - the United Self-Defence Forces of Colombia, which officially at least has demobilised.

BBC: Q&A: Colombia's civil conflict