Exaggerated: Every single secret society that ever existed (from the Freemasons to the White Lotus) is actually The Knights Templar in disguise. And they are also the true masters of every single government in history since Boethos and Gilgamesh.
Downplayed: The Knights Templar orchestrated the Thirty Years War and the American Revolutionary War.
An ancient rivalry among a group of people, all of them trying to foil each other's plans right up to the present day.
Subverted: The Templars get the bad rap because of, well, Knight Templar characters among them, who engage in little side projects like summoning the Anti Christ. However, except for those bad apples, their methods and goals are no worse than those of any other large, old institution.
The conspiracy started off with sinister aims or a particular goal, but as the world changed and the original founders died and moved into history, their successors gradually lost their way, drifting away or losing interest in the original goals until it eventually became unrecognizeable from what it started out as.
Nazi Germany propaganda, which depicted non-Germany-aligned nations as all part of an ancient conspiracy against Germany
The conspiracy is nothing bigger than the usual wheelin' and dealin' that happens in the background, and the groups aren't powerful enough to do whatever they want with the world.
However, a few opportunistic criminals get their hands on his research, find it profitable in a long run, and go ahead with the "Templars' Evil Plan".
Conspiracy Buffs are sent to Cuckoo's Nest insane asyla because the international Psychologists' conspiracy is a wholly owned subsidiary of the Ancient Conspiracy.
Plotted A Good Waste:
What starts off as a Conspiracy Thriller is soon revealed to be an accurate introduction into the world history, intended to raise the masses' awareness of it by wrapping knowledge into a fast-paced (if not overly complex) thriller plot.
Played For Laughs: Secret societies run so rampant that everyone is ultimately plotting against everyone. Nobody can so much as order a pizza without invoking a One Million Xanatos Pileup.
Played For Drama: The conspiracy is so good at what it does, nobody ever truly catches on. Tugging at the back of every sane person's mind is the thought that their Crapsack World is the result of collusion by wealthy elites, but those few that try to prove it are thoroughly crushed.