This question is very complicated, and it's all conjecture. One is that a new parallel space will be formed after crossing. Simply put, it is a beginning and two endings. For example, you crossed into the Anti-Japanese War, because you didn't have the July 7th, Nanjing Massacre and so on, but you wiped out the Japanese. But in another same space, time and place, it is normal anti-Japanese.

Another popular mechanism is the self-correction mechanism of history, that is, after you cross it, you can only change a small history, but the general trend of history cannot be changed. For example, crossing the Anti-Japanese War saved at most a few people, and some people died in the Nanjing Massacre. When you want to change the big historical trend, there will be some accidents, but it will make your change useless, that is, the self-correction mechanism of history. It allows small fluctuations, but there is only one main line.