Why was the five-kingdom system abandoned for a three-domain system?

The five-kingdom system was abandoned in favor of the three-domain system due to advancements in molecular biology, particularly the analysis of rRNA sequences. The five-kingdom system grouped all prokaryotes under the kingdom Monera, which was later found to be polyphyletic. The three-domain system, introduced by Carl Woese in 1990, recognizes the fundamental differences between Archaea and Bacteria, leading to a more accurate classification of life forms.