Different countries celebrate Mother’s Day on various days of the year because the day has a number of different origins. The celebrations (in one form or another) have existed for over a thousand years.
One school of thought claims this day emerged from a custom of mother worship in ancient Greece, which kept a festival to Cybele, a great mother of Greek gods. This festival was held around the Vernal Equinox around Asia Minor and eventually in Rome itself from the (15 March) to 18 March.
The ancient Romans also had another holiday, Matronalia, that was dedicated to Juno, though mothers were usually given gifts on this day.
In some countries the Mother’s Day began not as a celebration for individual mothers but rather for Christians as is now the case case in Britain and many parts of Europe.