The invention of microscopes made it possible to learn more about single-celled organisms, which led to the need for additional kingdoms beyond the traditional plant and animal kingdoms. As microscopes improved, scientists were able to see the complexity and diversity of single-celled organisms, which they realized could not be adequately classified as either plants or animals. This led to the creation of the kingdom Protista, which includes a wide range of unicellular eukaryotic organisms such as algae, protozoa, and slime molds. The development of other kingdoms, such as Fungi and Monera, followed as scientists continued to study and learn about different types of organisms. Therefore, the invention of microscopes was most responsible for creating the need for the additional three kingdoms.