This treaty is a global pact developed to protect threatened and endangered species from being caused further demise due to the import and export trade. The trade in animals and animal products was a multi-billion dollar industry and the hunting of animals was intense. This intensity caused populations to be reduced to the point where they were in danger of extinction.
Some examples are the rhino, tiger and gorilla.
These populations were so over-exploited, that recovery is not likely. Appendix I covers species that are endangered or extremely rare, and would almost never allow commercial export of such a species. Appendix II is for species that are not currently endangered but could be if trade or hunting is not regulated. A Convention export permit from the exporting country is required for these species. Appendix III regulates trade for species that are not endangered, but are being regulated by the export nation to prevent over-exploitation.