请教英语长难句For a while it looked as though the making of semiconductors,which America had invented and which sat at the heart of the new computer age,was going to be the next casualty.句子结构?which America had invented and which sat at the heart of the new computer age为the making of semiconductors的同位语,那么这个句子的主语是什么呢?it looked as though作什么成分?

主语：it为形式主语,the making of semiconductors为实际意义上的主语.
which America had invented and which sat at the heart of the new computer age是the making of semiconductors的定语而非同位语.
it looked as though是句子的（形式上）主谓结构.
全句分析如下：
For a while是时间状语
it是形式主语
looked是谓语
as though用于修饰谓语
the making of semiconductors是真正意义上的主语
which America had invented and which sat at the heart of the new computer age是两个并列的定语
was going to be the next casualty是系表结构