earlier是形容词，后面要接名词，可以改成early stage或者把earlier改成beginning。
it was as an...去掉as，forbodes改成forbade，其实evident也可以去掉。forbade后面改成the imminence of economic recession。one on another改为one after another。

Revised. Many thanks to @德鲁斯2012
In the early stage of The Great Depression, more and more people lost their jobs. This was a sign that foreboded the imminence of economic recession. And several months later, many companies went bankrupt one after another or were on the verge of bankruptcy.

别老急于用难词，你用那么多难词，然而还是很多语法错误，基础先打好。。。
earlier time 少了个time，it was an evident sign ,不用加as多此一举，it was an evident sign
that foreboded the imminence of economic resession,长句当中能用名词就用名词，没事儿别老从句套从句，forebode用过去式，我这就一个定语从句搞定。最后一句，一个接一个怎么是one on another,,,根本没这个用法我印象中。one by one就好。