Yvain notes in a blog post that governmental structures tend to be suited to the technology of the times:

And a lot of these late Neolithic/early Bronze Age cultures turned out the same way. If Ramesses II, Montezuma II, and Agamemmnon went to lunch together, they’d have a lot to talk about, despite being separated by continents and millennia. This suggests that the Generic Bronze Age Government – a god-king served by a bunch of warrior-nobles, plus massive militarism and slavery – probably just made sense given the circumstances.

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Countries that avoid liberal democracy usually regret it. China would be a good example. They tried being really Communist for a while and ended up becoming an economic basketcase. If they wanted to compete on the international stage they realized they needed a stronger economy, and so liberalized their market.

Thus, democracy as we know it may not in fact be a terminal value of government, but something that works well enough at the time. Or not.