A question's arisen from time to time in discussions I've had with people who discuss this sort of thing (i.e. weird guys with too much time on their hands) and rather than do the research myself (read: lazy bastard), I'd like to leverage the large number of people here from countries other than America to figure it out.

So the question is: What countries have a political system that predates that of the United States, is still in place today and has had few or no significant changes?

So, a few of the countries we've discussed were:

UK: compare the power of the Monarchy in 1790 to today -- I think there have been significant changes, yes?

France: French Revolution occurred after the American Revolution.

Germany: Had that whole Hitler-phase.

Japan: significant changes after WWII.

China: changed to communism

Russia: changed from Tsar to communist to democracy to ... not quite sure how to describe it today, help me out?

But these are countries that we, in the US, know a bit more about than others. I honestly don't know enough about, say, Switzerland or Sweden or Portugal history to say.

So a couple of the things we decided did not count as significant change:

Civil war where the political system and process afterward remained essentially unchanged from before.

Invasion and/or occupation where the political system and process returned to its prior state essentially unchanged.

Change brought about through the existing, established process (an example being amending the US Constitution).

Assassination -- unless the result was a change in political process, not simply leadership.

For clarification, I'm not claiming there are none that predate the US, I'm asking for assistance in identifying those that do.