It's not alternate history in those regards. It's just fiction. We wouldn't call Get Smart alternate history because Maxwell Smart didn't really exist in the 1960s.
Star Trek is alternate history in the fact that future history inevitably becomes alternate history. Khan wasn't on the cover of Time Magazine in 1997, nor did we get cryogenic sleeper satellites in the 2000s, etc. There's some things you can excuse, and there's some things that were clearly stated, did not happen nor can you even pretend reality and the fictional account somehow relate, so it is alternate history.
I think Star Trek-even in the 1960's-was more of an alternate history than a future history because of the whole Khan plot. Khan was supposed to have been born in the 1960's if I remember correctly-which means that Genetic Science must have been much more advanced in Star Trek's 1960's than the real 1960's-for whatever reason. That implies a divergence before the show was produced.
As I pointed out in the
Edith Keeler Lives: A Brief History and
The Eugenics Wars-A Brief History threads there is something really wonked about TOS' WWII.
Our first clue is in "City on the Edge of Forever":
In OTL both the atomic and V2 programs weren't really started until
after the United States declared war.
Germany's heavy water experiments were moving at a snail's pace because Hitler believed the war would end before they would be ready: "From the start of the war until the late fall of 1941, the German 'lightning war' had marched from one victory to another, subjugating most of Europe. During this period, the Germans needed no wonder weapons. After the Soviet counterattack, Pearl Harbor, and the German declaration of war against the United States, the war had become one of attrition. For the first time, German Army Ordnance asked its scientists when it could expect nuclear weapons." (
NOVA: Nazis and the bomb)
Because Germany only started looking at atom bombs in 1942 they were three years behind the US program which had started in 1939 and they never caught up--they only got to an early part the 1942 stage of Manhattan project in 1945. From what we can put together the best Germany could have produced in 1946 was a conventionally powered "dirty bomb" : "At best this would have been far less destructive than the atomic bombs dropped on Japan. Rather it is an example of scientists trying to make any sort of weapon they could i
n order to help stave off defeat." (
NOVA; Nazis and the Bomb)
Another problem is the V2. In OTL when Hitler was first show the plans for the V2 in late 1941 he was dismissive of the V2 as essentially an artillery shell with a longer range and much higher cost (Irons, Roy. Hitler's terror weapons: The price of vengeance. p. 181.) It was not until 1944
with German moral waning in the face of defeat after defeat that Hitler decided on building the V2.
In anything resembling OTL it is a catch-22 situation: a more successful Nazi Germany thanks to less US involvement would mean delaying both the German A-bomb (not really viable until 1948 under the best of conditions) and the V2 to carry it. So delaying US involvement in WWII essentually delays the very weapons that supposedly let Germany win the war!
Also the V2 of OTL simply didn't have the ability to carry an A-bomb...that is why Stalin put so many resources into duplicating the Superfortress instead of simply copying the V2 and slapping an a-bomb on top of it.
Now look at what Spock tells Kirk in "City on the Edge of Forever":
SPOCK: This is how history went after McCoy changed it. Here, in the late 1930s. A growing pacifist movement whose influence
delayed the United States' entry into the Second World War. While peace negotiations dragged on, Germany had time to complete its heavy-water experiments.
KIRK: Germany. Fascism. Hitler. They won the Second World War.
SPOCK: Because all this lets them develop the A-bomb first. There's no mistake, Captain. Let me run it again. Edith Keeler. Founder of the peace movement.
KIRK: But she was right. Peace was the way.
SPOCK: She was right, but at the wrong time. With the A-bomb, and
with their V2 rockets to carry them, Germany captured the world.
But removing the United States from the equation removes two of the big incentives for the Nazis to even go developing the bomb... or the weapon to carry it.
For anything in "City on the Edge of Forever" to make sense Star Trek's WWII
must be substantially different from ours before all the time travelers mess with it.
Our next clue is in "Patterns of Force" where John Gill, a Federation historian, says Nazi Germany "most efficient state Earth ever knew". Anyone who had bothered to read
The Rise and Fall of the Third Reich (1960) would know that claim was a load of garbage.
Nazi Germany was
spectacularly INefficient with incomparable programs duplicating effort (IIRC there were SIX rocket programs other then the Vengeance weapon one).
Other reviewers have pointed various problems with this episode
(
Star Trek – Patterns of Force (Review) and
Star Trek Re-Watch: “Patterns of Force”):
"It wasn’t efficiency but ruthlessness that enabled Hitler’s rise to power. Murdering or imprisoning each and every political enemy and exploiting and validating deep-seated xenophobia tends to consolidate power pretty damn effectively whether or not you have a team of industrial engineers creating a flawlessly organized state. The idea that a history professor didn’t understand or appreciate the complexity of that historical movement is unbelievable."
So either John Gill was a total incompetent in his field of history, stark raving bonkers (like nearly everyone else important in the Federation Kirk met), or TOS' Nazi Germany was
very different from the one in OTL.
Going back to Khan in TOS it is spelled out several times that he is the product of
selective breeding; but for that to make any sense the breeding would have had to started a long time before. Yes, the movies change it to genetic engineering but TNG and DS9 moved WWIII (ie the Eugenics Wars) to the mid point of the 21st century. Clearly the writers were trying to keep TOS complaint with our history but eventually they simply couldn't do it.