how to understand this sentence?

来源：学生作业帮编辑：作业帮分类：英语作业时间：2024/05/22 15:55:10

how to understand this sentence?
A disaster is an unforeseen mischance or misadventure(as a shipwreck,a serious railroad accident,or the failure of a great enterprise) which happens either through culpable lack of foresight or through adverse external agency and brings with it destruction ( as of life and property) or ruin (as of projects,careers or great hopes).
怎样理解which happens either through culpable lack of foresight or through adverse external agency and brings with it destruction?

which代的是A disaster.A disaster happens either through culpable lack of foresight or through adverse external agency and brings with it destruction
either……or……意思是不是……就是……
天灾的发生不是由于由该受责备的缺乏远见就是由于不利的外部影响所带来的破坏

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