Before 2105 AD: During the middle 21st century, the Buy n Large corporation assumed control of the planet's entire economy, including various world governments.
2105 AD: The population had reached to around 200 billion. After Buy n Large gave the right for everyone to spend and buy, the planet soon came to the position that there was no place to properly dispose the waste. After Buy n Large failed to dispose all that trash they created an "amazing plan", that they thought the best and would work, called "Operation Cleanup". The plan was to evacuate all of the population (except some who stayed behind for maintenance) away in different regions of space.
Whilst back on Earth, WALL•E (Waste Allocation Load Lifter: Earth class) robots and huge mobile incinerators would take charge of cleaning up. Thousands of Starliners, including the Axiom, were built all around the world, so that people would live safe and happy far from "Home" in the comfort and the luxury of the Starliners. Operation Cleanup success would be followed by "Operation Recolonize". However back on Earth the toxin levels began rising and many WALL•Es were faiIing. After the CEO of BNL that time Shelby Forthright saw that his plan was failing and everything was becoming worse, so he ordered all of the WALL•E robots to be shut down (except for one) and to evacuate all of the remaining population left. He also secretly sent the A113 Directive to all Autos in the year 2110 to cancel Operation Recolonize as he deemed that Earth would never support life anymore.
Earth was left without population, and the toxins also destroyed all plant and animal life (although it's possible that some animals survived somehow). Aboard the Starliners, over the centuries, each new generation of humans grew more and more obese, losing bone mass in the process, due to over exposure to micro or artificial gravity and instead relying on hover chairs for to move around the ships. They also started to forget about "Home".
2805 AD: The last remaining WALL•E unit continued to obey his directive every day and doing the same job over and over: creating small cubes from trash and building colossal towers from them, while there were no humans to start the incinerators. Earth was covered in trash and suffered from sandstorms and torrential downpours. One day, however, the Axiom (one of the biggest BNL Starliners ever made) sent out a probe ship to Earth in the exact city where the Axiom was launched over 700 years ago. An EVE unit (Extraterrestrial Vegetation Evaluator) was deployed from the probe ship and began an operation in search of plant life.
The unit was successful in finding an example of positive plant life with help of the last WALL•E. The plant caused the unit to shut down which alerted the probe ship to come back for transport to the Axiom. This plant was successful and proved that plants where indeed growing in city ruins. The plant was placed in the holodetector so that the Axiom made an automated hyperjump back on Earth. Later after these events, humans began rebuilding again with the help of robots making Earth cleaner and greener as ever before.