When do christian countries start counting their years?

Christian countries typically start counting their years from the birth of Jesus Christ, which is designated as the year 1 AD (Anno Domini). The system was developed in the 6th century by the monk Dionysius Exiguus, who aimed to establish a calendar based on the life of Christ. Years before Christ's birth are counted as BC (Before Christ). This method of timekeeping became widely adopted in Europe and has influenced the Gregorian calendar used by many countries today.