I've been fascinated by Anakin's statement in Phantom Menace that he dreamt he was a Jedi and "came back and freed all the slaves". What if this happened instead and was the crisis/ catalyst that started the Clone Wars and began Anakin's downfall? I suggest we see Anakin as a three-year old (perhaps) then at age ten or twelve then he leaves the Jedi Temple as part of the Trials. Around this time Palpatine is close to the (or head of) the Galactic government. He befriends Anakin and confides that Anakin's mother sold him to the Jedi Order to pay off her debts to the Hutts.

When we next hear about Anakin, the Senate is in uproar over a slave rebellion and commissions an army to either quell the rebellion or retake several hundred systems which seceded in protest at the Senate's inactions. It transpires that Anakin is (one of) the leader(s) of the rebellion which causes Kenobi to be expelled from the Jedi Order (more dramatically he could even turn to the Dark Side).

This scenario perhaps allows the Senate to issue a bounty on Kenobi which is taken up by Jango Fett. Kenobi escapes after killing Fett and orphaning Boba, which leads to him discovering the army of Fett clones purchased/commissioned on the Republic's behalf. Meanwhile, Palpatine contacts Anakin and convinces him that his rebellion is futile. Through a convoluted series of events, Anakin discovers Palpatine is also Darth Sidious. This leads him to renounce the rebellion and convince his followers to re-join the Republic. Meanwhile, Kenobi locates and confronts Anakin, which results in Anakin's permanent injuries and his acceptance of the Darth Vader persona. The reason for this is simply because Kenobi and the Jedi have no knowledge of Anakin's surrender and Palpatine's alter ego; moreover the Jedi would not inform Kenobi of any updates on current affairs while he goes off on his "idealistic crusade". Anakin's rebel ex-slaves join with the surviving clones in forming the bulk of the Imperial military.

As an addendum, Sidious deliberately sets up the Alliance to Restore the Republic hoping (or predicting) that a potential apprentice will kill and replace Vader-either through fearing that Vader will overthrow him or that Vader would soon prove unsuitable as a successor to the Sith legacy.