Even the US had a close call with a fairly nasty civil war in that time frame, and in three days the 198th anniversary of the Burning of Washington happens: http://en.wikipedia.org/wiki/Burning_of_Washington "On August 24, 1814, after defeating the Americans at the Battle of Bladensburg, a British force led by Major General Robert Ross occupied Washington, D.C. and set fire to many public buildings. The facilities of the U.S. government, including the White House and U.S. Capitol, were largely destroyed."

Thailand.

I think I could argue that England has been pretty stable since at least the end of the Civil War - which is 360 years ago. A lot of the institutions that form part of the current UK go back an awful lot further than that.

[NB I'm not English]

I'll reject your democratic requirement out of hand, as democracies haven't proven particularly stable. There was that trial-run in Athens which lasted 501 years (508 - 7 BCE, with interruptions). Other than a few small/outlying instances (most notably the Althing in Iceland, it didn't re-emerge until the short-lived Corsican Republic (1755), and of course, the United States (1776).

Japan (660 BCE) and China (221 BCE) have both had feudal / bureaucratic governments exhibiting very high levels of stability. While dynasties and eras are marked, the overall states persisted largely intact.