求小伙伴们帮解答prep07阅读的一个句子结构~ 没看懂~

750狗狗狗

来自于prep07阅读2的第8篇。句子如下：
as unions reached the peak of their strength in the 1940s, the community base that had made their success possible and to which women's contributions were so vital became increasingly irrelevant to unions' institutional life.
没看懂... 求问句子结构。。谢谢~

750狗狗狗

自己顶一下。。。有没有人哇。。。求帮忙哇。。。 圣诞快乐哇。。。