The problem with this thread is that the criteria are too vague. If we count the subordination of San Marino to the Italian fascists as being a substantial change in government, then I would say the longest continuous state would be the United Kingdom, which has not had a revolution since 1688 or a civil war since 1708; unless you count the partitioning of Ireland in 1922, in which case a better example might be the United States, which has had a continuous government from 1789, with the exception of the American Civil War in 1861 (are we counting that?), etc...