The earliest Mother's Day celebrations can be traced back to the spring celebrations of ancient Greece in honor of Rhea, the Mother of the Gods. During the 1600's, England celebrated a day called "Mothering Sunday". Celebrated on the 4th Sunday of Lent (the 40 day period leading up to Easter*), "Mothering Sunday" honored the mothers of England.
As Christianity spread throughout Europe the celebration changed to honor the "Mother Church" - the spiritual power that gave them life and protected them from harm. Over time the church festival blended with the Mothering Sunday celebration . People began honoring their mothers as well as the church.
In the United States Mother's Day was first suggested in 1872 by Julia Ward Howe(who wrote the words to the Battle hymn of the Republic) as a day dedicated to peace. Ms. Howe would hold organized Mother's Day meetings in Boston, Mass ever year.
In 1907 Ana Jarvis, from Philadelphia,began a campaign to establish a national Mother's Day. Ms. Jarvis persuaded her mother's church in Grafton, West Virginia to celebrate Mother's Day on the second anniversary of her mother's death, the 2nd Sunday of May. By the next year Mother's Day was also celebrated in Philadelphia.
Ms. Jarvis and her supporters began to write to ministers, businessman, and politicians in their quest to establish a national Mother's Day. It was successful as by 1911 Mother's Day was celebrated in almost every state. President Woodrow Wilson, in 1914, made the official announcement proclaiming Mother's Day as a national holiday that was to be held each year on the 2nd Sunday of May.
While many countries of the world celebrate their own Mother's Day at different times throughout the year, there are some countries such as Denmark, Finland, Italy, Turkey, Australia, and Belgium which also celebrate Mother's Day on the second Sunday of May.
Reference: www.holidays.net/mother/story.htm