As Europe became Christianized, these holidays, Beltrane and Walpurgis Night, lost their religious character and became popular secular celebrations, such as in the case of May Day; or these celebrations were merged with or replaced by new Christian holidays as with Christmas, Easter, Pentecost and All Saint's Day. There has been, a re-embracing of these holidays and their religious importance by the European and American neopagan movements in the 20th and 21st centuries.
In many countries, May Day is also Labor Day. This originates with the U.S. labor movement in the late 19th century. On May 1, 1886, unions across the country went on strike, demanding that the standard workday be shortened to eight hours. The organizers of these strikes included socialists, anarchists, and others in organized labor movements. Although many of these protests were not immediately successful, they proved effective eventually, as eight-hour work days eventually become the norm. Labor leaders, socialists, and anarchists around the world took the American strikes and their fallout as a rallying point, choosing May Day as a day for demonstrations, parades, and speeches. Labor Day is still celebrated on May 1st in countries around the world, and it is still often a day for protests and rallies.
So happy May Day to you no matter how you choose to celebrate it!