If Okabe deletes the D-Mail log from Echelon, SERN doesn't find it.
If SERN doesn't find it, the Rounders don't raid the Future Gadget Lab.
If the Rounders don't raid the Future Gadget Lab, SERN doesn't get the advantage in the race to perfect the time machine.
If SERN doesn't get the advantage in the race to perfect the time machine, SERN doesn't get to form a dystopia.
If SERN doesn't get to form a dystopia, Daru doesn't get killed before he completes the C-204.
If Daru doesn't get killed before he completes the C-204, Suzuha doesn't get sent back in time with a faulty time machine (the FG-204).
If Suzuha doesn't get sent back in time with a faulty time machine, the time machine doesn't crash into Radio Kaikan.
If the time machine doesn't crash into Radio Kaikan, Doctor Nakabachi's time machine lecture doesn't get canceled.
If Doctor Nakabachi's time machine lecture doesn't get canceled, Kurisu brings the time travel thesis to Radio Kaikan to show it to Doctor Nakabachi.
If Kurisu brings the time travel thesis to Radio Kaikan to show it to Doctor Nakabachi, she gets killed.
If Kurisu gets killed, Doctor Nakabachi gives the thesis to the Russians.
If Doctor Nakabachi gives the thesis to the Russians, WWIII happens.