I think context will be very important for understanding this sentence. When "One people" is used like this, it means that we are all the same group, and might be a call for unity. For a small example, if different people from the US are arguing about an issue, someone might say "We are all one people" as a call for unity, saying that our differences are small in comparison to what holds us together - we are all Americans. In the broader sense, it can be used of you and I. You are Chinese, and I am American, but our differences are small as we are all one people - what is different about us is small compared to what is the same about us. We should be able to put our differences aside and be united in purpose as we are all very similar - we are all one people. There can be other meanings, but I think this would be the most common general meanings.