Meanwhile, Padme Amidala (Natalie Portman) reveals that she is with child, and this revelation terrifies Anakin, for he has been experiencing terrible visions (like the one about his mother, in Attack of the Clones.)
Eventually, feeling he has no option, Anakin succumbs. He betrays the Jedi Order but in doing so, no longer remains the man that Amidala loved. On opposite sides of the war now, Obi Wan and Anakin duel, and Obi Wan wins, leaving a hobbled, burned Anakin to die on the side of a volcano on the planet Mustafar.
What has happened to the Republic? Well, to face a grave and gathering threat (the Separatist movement), the Senate voted for the creation of a "standing" clone army to fight evil renegade Count Dooku. In thousands of years (and presumably having vanquished many other threats), the Republic never required such an army, but rather was safeguarded by the noble protectors of peace, The Jedi Knight.