The first country to adopt the Gregorian Calendar was Italy, specifically the Papal States, in 1582. Pope Gregory XIII introduced this calendar as a reform to the Julian Calendar, which had accumulated inaccuracies over the centuries due to the miscalculation of the solar year. The Gregorian Calendar corrected this by establishing a more accurate system of leap years, leading to better alignment with the seasons. Though initially adopted by Catholic countries, this calendar gradually spread around the world and is now the most widely used civil calendar globally, replacing the Julian system in various nations over subsequent centuries.