Initially, all of the bacteria has been classified in the same kingdom, monera. The main reason for this was that when this classification was made, the scientists only had so much information about the bacteria that it seemed to them that they are all part of the same kingdom. As the technology developed and enabled the scientists to study the bacteria much better and in much greater detail, it turned out that the classification was wrong. A new classification then came out which separated the bacteria into two kingdoms, bacteria, and archaebacteria based on their characteristics of course.
