I rekon Nazism is the one that first jumps to mind. Like someone mentioned earlier, it is a great shame about some of their ideologies, as they certainly turned Germany around, however it is debatable about a LOT of the things they did, and if the people really wanted it, or they had just been brainwashed by Goebells, the Propaganda genius. Howveer my 6th form History teacher did point out today that even if Nazism had survived the second world war, it still wouldn't have lasted as it was just so chaotic, it would have imploded.
Oliver Cromwell and the abolishment of Monachy in the UK for 13 or however many years is another one that jumps to mind.