作者无法通过中国的历史比美国更悠久这个证据来得到中国比美国更好的结论。作者unfairly assumes that 历史更悠久的国家就更好。
you can combine this two sentence into one, if what you what to express is as simple as this example..
using something, like, the speaker asserts China is better USA based solely on that fact that the former one has longer history that the latter, however, longer history is insufficient to support his xxxx.
but when assumption is more complicate, it is ok for you to repeat...