Charlemagne reunited Western Europe. He built an empire that reached across three countries.
The answer is "wanting to disguise the truth they have uncovered."
Some historians find this tough. One of the reasons would be because not all people may or may not, like the truth. Some historians would omit some part of the truth to keep violent reactions from the readers or outsiders.
The demand for slave increased because Growing rice required much labor, and the demand for slave labor rose. both have something to do with money.
