The Future was started when three villains - Drakken, Monkey Fist and Duff Killigan - joined their forces to defeat Kim Possible once and for all. Understanding that they could not defeat her in the present day, they decided to transfer efforts in past and take her out there, in a time when she was not so experienced at fighting them. They believed that they could easily neutralize her in her past and essentially erase their defeats at her hands.
By using a mystical artifact known as the Tempus Simia, another element of Mystical Monkey Power, they were able to open portals through time and space. Their first plot, which was primary Drakken's, was to find a younger version of Kim Possible in past, and break her - mentally or physically, so that she never became a heroine. The team of villains made two attempts, but neither plot succeeded. They actually backfired, as Preschool Kim was able to defend herself as well as defend her new four-year old friend, Ron Stoppable, who she has just then met.
The second plan was thwarted when a time-traveling present day Kim Possible, with help from Future's Resistance member Rufus 3000, arrived to intervene in her pre-teen years when they attempted to simply kill Kim in Paisley's Mansion, and Rufus 3000 brought in Ron Stoppable to solidify the victory.
However, while the battle over Kim's past was fought, a third party intervened: the future version of Shego had arrived to Kim's first mission and instructed her present version on how to take over the world, thus ensuring the future as Shego escaped from the failure to kill pre-teen Kim with the Tempus Simia.
With the Tempus Simia in her possession, Shego moved through time to lay groundwork for her evil scheme by getting big into dot coms, opening a bank, and established an evil think tank for various mind control and ray based weaponry. With the groundwork laid and a sturdy base to begin her plot, she began to, ironically enough, establish events that allowed temporal manipulation in the first place.
In the first stage on her plot, Shego had to disable Team Possible. Being a multi-millionaire, she used her influence to transfer Ron's mother in Norway, forcing the entire family to move. Without Ron and Rufus to assist, Kim was unable to successfully engage and defeat the team of Drakken, Monkey Fist, Killigan, and the as-of-yet unaware Shego. With the origin of her entire plot secure, Shego could now begin her plan in earnest.
Thanks in addition to the future's Resistance forces sending Kim (and later Ron and Rufus) back in time, presumably meaning none of them were present when the actual takeover occurred, Shego succeeded in taking over the world with a campaign that was described by Rufus 3000 as occurring with "cruel swiftness", leaving no one but those involved with an idea of what had happened. Shego had successfully taken over the world by 2010 at the latest.
Kim Possible: A Sitch in Time has this. Shego stole the time monkey only because she stole it, went back in time, transferred Ron away from Kim, and then told herself to steal the time monkey. This somewhat changes when the time monkey is destroyed and the entire timeline that its use created is revoked, along with the very existence of the time monkey. So, you destroy it once, it erases itself from ever existing. So Shego never went back in time, Ron never left KP, and nobody ever knew or cared about the time monkey.
- And within that wheel, Shego takes the monkey while in the past and escapes into the timestream, so Kim goes straight from the past to face Shego in the Bad Future. Shego manages to Take Over the World partly because Kim wasn't around to stop her, since she skipped over that whole time.
- On the other hand, the self-destruction of the time monkey is only implied; if its destruction doesn't affect its past existence, then the movie becomes a case of the Timey-Wimey Ball.