While historians agree on this, what they can’t agree on is a uniform way to determine which country is the oldest. According to HowStuffWorks, if you define a country’s “birth” by analyzing documented government or civilization size, Egypt, Iran, and India take the top three spots. And if you measure by the oldest constitution, the United Kingdom, San Marino, and the United States rank as the oldest. Let’s take a closer look at the oldest country in each category to learn more about the world. UNITED KINGDOMUnited Kingdom | akinbostanci/GettyImagesOldest ConstitutionThe United Kingdom adopted its “first constitution” in 1215: the Magna Carta.