Alt history is a subject I have been fascinated by for a number of years, but only really made a serious attempt at recently.

It's easy to do poorly, and I have some thoughts on how to do it well.

First, study history, and I don't just mean watch a bunch of documentaries. Documentaries tend to adhere to a very biased interpretation of history and although they can point you in the direction of things to research, they shouldn't be your only source. Identify firsthand sources from the era you are studying, and pay attention not only to facts, names, and dates, but also to the tones, opinions, aspirations, and biases of that era. Read editorials, speculations about future events, and newspaper articles and ads. If it's a 20th century piece, immerse yourself in the music, films, and popular culture of that era. Get to where you can fully immerse yourself in any given situation in the era you're focused on, the primary players involved, and how they might react if things happened differently.

You can always tell when someone has derived their entire scenario from badly biased sources, or when they know the facts and dates but don't understand the people or their motives. More often than not this is how bad polemics are written.

Second, pick your point of divergence. One way to choose your point of divergence is to decide what the defining difference of your new timeline will be, then extrapolate an intermediate history for that by changing things in reverse order, as I did for the space programs in "The Vimana Incident." Another way- probably the more solid way- is to choose your point of divergence first and then extrapolate how the world would be different.

You can have one point of divergence- as in the assassination of FDR in "The Man in the High Castle." In this scenario, Philip K. Dick imagines a domino effect starting with the election of politicians who remain isolationist in WW2. He studies the players involved and their motives, means, and opportunity to make their mark on this world, then extrapolates a new world accordingly. In the case of one point of divergence, multiple threads lead to additional points of divergence.

You can also have multiple points of divergence, however. In the case of multiple points of divergence, each point must happen as an independent development not directly affected by the other points, which then converge into a "perfect storm."

In the case of "The Vimana Incident," I had three points of divergence. The first was in 1916, with hybrid rocket technology being invented as a result of experiments in a British munitions lab. As a result, military rocket technology not only becomes operational by the Battle of the Somme, but is fostered and developed. By contrast, in our timeline, the first rockets were liquid-fueled and were tested ten years later, during the inter-war years. The lesser efficiency of the liquid-fueled rocket and its invention in peace time meant that it was largely ignored, outside of Germany. As a result, by the 1940s Germany had operational military rockets. Giving the British an operational military rocket years earlier in WWI changes the political and technological landscape significantly. The war ends a year earlier and the US is never a major player.

The second point of divergence is in 1934. Rather than remaining under wraps until the 1970s as it did in our timeline, War Plan Red- an actual, real plan for war with the British Empire- is leaked within a year of its publication. This leads to an even more desperate attempt to reconcile Anglo-American relations, which ultimately leads to the space program.

The third point of divergence is in 1935. Magnetic tape has not only been invented a few years earlier, but is actually used for computers before it is used to record audio, thus allowing computing technology to advance to sufficient levels to launch lunar missions.

Finally, a thought: conspiracy theories can make for great fiction, especially if they're well put-together. However, history on its own is often interesting enough to not need embellishment. As to whether or not to add conspiracy theory material to your book, ask yourself if it is really necessary to move the story forward, or if you can move the story forward just fine without it. Simply adding them for wow factor won't impress anyone.