句子翻译和理解

Famous explorers of the North American frontier, Lewis and Clark had experienced great difficulty finding game west of the Rockies and not until the second of December did they kill their first elk.
我的问题是不知道not until the second of December did they kill their first elk.怎么理解，谢谢

北美边远地区著名的探险家们——Lewis和Clark在落基山脉西部找寻猎物时经历了巨大的困难，直到十二月的第二天他们才杀死他们的第一头美洲赤鹿。

楼上几位对于最后一句为您做的语法结构分析已经够完整啦，我唯一要补充的是这句话该怎么去理解： their fear -as mine was until my father’s letter -is of being a disappointment 他们（指孩子们）的恐惧，和我在还没接到（或读到）我父亲的信之前如出一辙，就是不想让人失望。 让谁失望呢？很显然的让家长失望。 下面是整段的翻译： a long way from 12 now , i realize he would have been proud when i made any progress. lately, though , i’ve come to belvieve he would want me to move on to what comes next : to be pround of , and believe in , somebody else . tt’s time to start writing my own letters to my children . our children look to us with the same unanswered question we had . our kids don’t hold back because they’re afraid to fail. they’re only afraid of failing us . they’re only afraid of failing us . they don’t worry about being disappointed . their fear -as mine was until my father’s letter -is of being a disappointment . 现在离我12岁已有好长一段时间啦，我确信他一定会为我的进步感到骄傲的。但是近来我越来越相信他会期许我向下一个目标推进：去相信别人，以别人为荣。该是我开始给自己的孩子们写信的时候啦。我们的孩子带着我们当初一样的疑虑在看我们，他们并不会因为害怕失败而却步，他们只担心表现不好让我们蒙羞，而并不怎么担心自己的得失。他们心中的恐惧，和我在没读过父亲的信之前如出一辙，就是不想让人失望。 注：写这段文字的时候，作者的父亲自然早已去世了。从 would have been proud 和 he would want me to move on 的语态中显而易见。个人猜测这封他父亲留给他的信是最后的遗物，在他12岁时父亲遭遇不幸身亡。 希望能给您的学习和理解带来一些帮助。