HEY! Watch the TS spoilers, it's not opened everywhere yet!
it's a loop. Randall Frakes says as much in the T1 novelisation, citing Ourobouros, the snake eating its tail.
Reese had the photo of sarah and fell in love with her, leading to him volenteering to go back, leading to him getting her pregnant, leading to the photo of her wistfully thinking of him, leading to him falling in love with her...
and like hyzmarca said, she had to have known about the war to train John to storm the camps and smash the metal and liberate the slaves.