请教一个句子！

jojofgasw

Japan used the huge sums of capital it received from the US after the Second World War to hepl build a modern indusrial system.

其中的"it received from the US after....War" 是做什么成份修饰前面的"capital"的呢？同位语？定语从句？

如果把it去掉这句话还对么？如果是同位语的话，需要在it前面加逗号么？

谢谢大家.