Though one might assume Mother's Day was invented by the major greeting card companies it was actually around in ancient Greece as a celebration of the mother of the gods.
In the United States Mother's Day was started as a day for social activism and an outcry for peace by Julia Ward Howe after the Civil War. Her attempts to get Mother's Day recognized failed.
Anna Jarvis in 1907 began crusading for a memorial day for women. Her efforts were in part to honor her own mother who worked to improve sanitary conditions for both sides of the Civil War by organizing Mothers' Work Days.  The first Mother's Day celebration was in Grafton, West Virginia, May 10, 1908 in the church where Anna Jarvis taught Sunday School. Jarvis would later oppose the commercialization of the holiday.
President Woodrow Wilson declared the first national Mother's Day in 1914 as a day for Americans to show the flag in honor of mothers who had lost their sons in war.  Mother's Day is one of the most commercially successful holidays in the United States.

History of Mothers Day

Anna Jarvis of Philadelphia is credited with bringing about the official observance of Mother's Day. Her campaign to establish such a holiday began as a remembrance of her mother, who died in 1905 and who had, in the late 19th century, tried to establish "Mother's Friendship Days" as a way to heal the scars of the Civil War.

Two years after her mother died, Jarvis held a ceremony in Grafton, W. Va., to honor her. She was so moved
by the proceedings that she began a massive campaign to adopt a formal holiday honoring mothers.

1910
West Virginia became the first state to recognize Mother's Day. A year later, nearly every state officially marked
the day.

1914
President Woodrow Wilson officially proclaimed Mother's Day as a national holiday to be held on the second Sunday of May.

1923
But Jarvis' accomplishment soon turned bitter for her. Enraged by the commercialization of the holiday, she filed a lawsuit to stop a 1923 Mother's Day festival and was even arrested for disturbing the peace at a war mothers' convention where women sold white carnations -- Jarvis' symbol for mothers -- to raise money.

"This is not what I intended," Jarvis said. "I wanted it to be a day of sentiment, not profit!"

1948
When she died in 1948, at age 84, Jarvis had become a woman of great ironies. Never a mother herself, her maternal fortune dissipated by her efforts to stop the commercialization of the holiday she had founded, Jarvis told a reporter shortly before her death that she was sorry she had ever started Mother's Day.

She spoke these words in a nursing home where every Mother's Day her room had been filled with cards from all over the world. Today, because and despite Jarvis' efforts, many celebrations of Mother's Days are held throughout the world.

Although they do not all fall at the same time, such countries as Denmark, Finland, Italy, Turkey, Australia and Belgium also celebrate Mother's Day on the same day as the United States.