The Vatican is the smallest country in the world. However, it is not the oldest as it has only been in existence as a country since 1929. The oldest country in Europe is hard to determine since boundaries, names and governments have change so frequently over thousands of years. Your question would have to declare what basis is to be used. For information on the oldest countries in the world, see the link below.
Vatican City
The Republic of San Marino is the smallest republic in the world.
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Vatican City, in Rome, Italy. It has an area of 0.2 square miles and is the center for the Roman Catholic Church.
Republic of Congo
The smallest republic in South America is quite a common crossword clue. The answer to this clue is the country Surinam.
San Marino is the tiny country located in the Italian peninsula that is the smallest republic in the world. It is known for its picturesque landscape and historic sites, including the UNESCO-listed old town.
Tuvalu has the smallest GDP of any country. The Democratic Republic of the Congo's citizens have the smallest average income of any country.
Despite being the second largest country in the continent, the Democratic Republic of Congo has the smallest coastline at 37km
The Republic of the Maldives is the smallest Islamic country in the world and the smallest country in the world. The population, as of October 2009, is 304,000 individuals out of them 98.4% are Muslims. See the related link for more information.
Vatican City is the world's smallest country, however it is not democratic, it is an absolute monarchy. The second smallest country, Monaco, is the smallest partial democratic state in the world, it is a constitutional monarchy (republic/monarchy). The smallest absolute democratic state in the world would be Nauru, which is the 3rd smallest country.
Vatican City is the smallest nation on earth, so Nauru is larger. Nauru is the smallest republic on earth.