In my mind...
Episode I=45 Years BBY
-Obi-Wan discovers Anakin, who begins his training as a Jedi
-Clone Wars begin.
Episode II=40 Years BBY
-Clone Wars end.
-Republic becomes Empire.
-Palpatine becomes Emperor.
-Jedi Knights are exiled and relieved of their duties to the Republic, however they are not yet Purged.
Episode III=20 Years BBY
-Shows Anakin in exile with wife. She is pregnant but wishes the tell husband of the good news for a latter time.
-Shows Obi-Wan with Yoda on Dagobah. Yoda feels a great disturbance in the Force foreseeing great terror and darkness in the future.
-Most other Jedi Knights with family ala Anakin.
-Empire has been gradually degraded and more totalitarian in the past 20 years as Obi-Wan discovers after leaving Dagobah. Emperor is found to be a Dark Sider.
-Obi-Wan recruits surviving Jedi to prepare an "Alliance to Restore the Republic" with Mon Mothma, Garm Bel Iblis, Bail Organa, and other political leaders. Finally, he finds Anakin, the most powerful lightsaber duelist, who takes it upon himself to confront The Emperor, personally, rather than be patient and go along with Obi-Wan and the burgeoning Alliance (ala Luke going off to face Vader in ESB).
-Anakin is lured to the pull of the Dark Side of the Force as The Emperor teases him with the power of the Dark Side, convinces him that The Empire is the only way to pave Galactic peace and security, and shows that the Jedi are Rebels fermenting a further war.
-The Emperor orders the newly declared Lord Darth Vader to go out with a legion of the most elite Stormtroopers and exterminate the Jedi Rebels.
-Obi-Wan feels a great disturbance in The Force and heads off to Dagobah for safety and for further illumination in his feeling from Yoda, the latter of whom reveals that Anakin has fallen to the Dark and the both of them feel only two Dark Forces lingering left in the Galaxy, where there was once a thousand light speckles (i.e. The Jedi have been wiped out and they feel it).
-Yoda faces the Emperor, and Obi-Wan hunts down his old pupil and friend.
-Yoda and The Emperor duel only using the Force (no sabers for them) and result in a draw with Yoda going back to Dagobah, where he's resided for over 100 years.
-Obi-Wan finds Vader on Mustafar (or whatever one wants to call it) and duels him until he has fallen into a Molten pit. He sees him crawl out, but cannot kill his old friend.
-Before Yoda goes to Dagobah, he meets up with Kenobi and the Founders of the Rebellion telling them that he senses two new "lights" in the Galaxy that could be possible Jedi survivors. Hoping that they are far-flung powerful Jedi, they instead find (relatively) nearby Illuminations in the Force on the same planet where Anakin had been with his wife for 20 years. There they find that Anakin's wife has given birth to twins, both with great force potential. Yoda tells Obi-Wan to take the boy in exile with to live with his brother Owen on Tatooine, which is far-away enough to attract further Imperial attention. Bail Organa offers to take the Mother and Daughter to live with him and his wife as a disguised hand-maiden (Mom) and an adopted daughter of the infertile Royal Couple (Leia)
-Yoda goes back to Dagobah for the rest of his life.
-Obi-Wan in Tatooine with Luke, Royal Family on Alderaan with Leia.
-Darth Vader placed in his iconic life-preserving suit of armor and respiratory helmet and The Empire now has NO restraints holding it back from unleashing further terror except for the Imperial Senate...
...two kids, two Old Wizards, and a burgeoning Rebel Alliance!