not only开头+ because后面接的句子要倒装吗

不需要,因为现在在重点转到because上面了,按照正常的句子顺序写出来就可以了.
例如：
That is not only because England is the first country that has constitution,but also the constitution of England has its bright characteristic.
讲起宪政必言英国,这不仅是因为它产生最早,而且特点鲜明、独树一帜.
当然你也可以用not only because of +名词的句型,这样也可以~