The Terminator Saga Multi-Universe explained...

[Uncle Entity]

UNIVERSE 1: CAUSAL LOOP (T1/T2)

Fixed timeline. The time travellers and their actions have always been part of history.

1965: Sarah Connor is born.
May 1984: "The Terminator". Skynet and John Connor are conceived.
1985: John Connor is born.
1993: Sarah Connor is arrested.
March 1995: "Terminator 2: Judgement Day".
1996: Neural net chip is built from "secret" back-up work and a new team of scientists who retrieved Miles Dyson's studies.
1997, 29th August: Judgement Day happens.
2000s: Kyle Reese is born.
2027: Kyle and John met for the very first time.
2029: Skynet is defeated. John sends Kyle and "Uncle Bob" T-800 back in time.


UNIVERSE 2: REVISABLE TIMELINE (T3)


FUTURE 1:

2029: John Connor I sends Kyle Reese back to May 1980. This future is erased when past is changed by Kyle Reese and "Evil" T-800.

FUTURE 2:

2029: John Connor II (son of Kyle and Sarah) sends "Uncle Bob" T-800 back in time. This future is erased when past is changed by Uncle Bob and T-1000. Judgement Day is "postponed" to 2004.

FUTURE 3:

2032, 4th July: John Connor II is killed by T-850.
2033, 28th October: T-X and T-850 are sent back in time.


1959: Sarah Connor is born.
May 1980: "The Terminator". John Connor II is conceived.
1981: John Connor II (Nick Stahl) is born.
1992: Sarah Connor is arrested.
1994: "Terminator 2: Judgement Day".
1997: Sarah Connor dies of leukemia.
2004, 24th July: T-X and T-850 arrive in the past. The third and definitive Judgment Day happens.


UNIVERSE 3: Terminator Salvation

In this universe, John Connor looks like Christian Bale.

2003 - Project Angel. Cyberdyne drops the ball, and CRS is now the main chief of the Skynet project.
2018 - Terminator Salvation. John Connor II battles Skynet (CRS Product) to save Kyle Reese. Hybrids like Marcus Wright are also introduced.


1- Salvation is not the third iteration of the future events, but the fourth. When JD 2004 Skynet (2033) sent the Terminatrix back, this caused a new alteration. Indeed T-X comes from a different iteration, a third future where: a) John Connor II's Tech-Com lieutenants are different guys (the boys and girls T-X kills in the past); b) John Connor II dies on July 4th, 2032.
Both T-800 and T-X come from October 28, 2033.
Now, in Salvation, JD 2004 Skynet (2018) is just the "younger" version of the JD 2004 Skynet (2033) which sent back the T-X. Both are the third Skynet, just at different stages/times.

2- In Salvation, Kyle Reese CAN die. That doesn't imply John Connor II will cease to exist at all. John Connor II is son of Sarah and JD 1997 Kyle Reese ---> NOT JD 2004 Kyle Reese. JD 1997 Kyle Reese ALREADY exists in 1980, and he comes from the "original" ITERATION of the future. This also means that John Connor II should not send JD 2004 Kyle Reese back in time, since this would result into two Kyle Reeses operating in 1980. Disaster.

3- In Salvation, JD 2004 Skynet (2018) must have collected infos about the three Terminators operating in the past, those coming from previous iterations of the future (T-800, T-1000, T-X). That's why in 2018 JD 2004 Skynet plans a new "gimmick" in order to kill John Connor II: Marcus Wright. In the third future, JD 2004 Skynet (2033) never used Marcus Wright, which wasn't even completed (I guess). Marcus represents an important point of divergence, since he helps John destroying the T-800 series which will indeed never be launched as it occurred in the three previous futures.


UNIVERSE 4: THE TV SERIES.


UNIVERSE 5: T1-T2 UNTEMPERED CAUSAL LOOP BEFORE "GENISYS".

Fixed timeline/causal loop until the arrive of T-3000 in 2029.
In this universe, John Connor looks like Jason Clarke and so on...


UNIVERSE 6: Unknown timeline which generated the T-3000/Skynet (Matt Smith) that later travelled to Universe 5 (Year 2029) and caused "Terminator Genisys" to happen.