请问下面这句话中by代表什么意思,it指代什么,

题目

请问下面这句话中by代表什么意思,it指代什么,
There was no flinching and no thought of giving in; and by what seemed almost a
miracle to those outside these Islands,though we ourselves never doubted it,we
now find ourselves in a position where I say that we can be sure that we have
only to persevere to conquer.

答案