The history of labor union in the United States knew its beginnings in the 19th century, when workers realized that they need organization in order to seek better conditions, confront the extremely lax laws of the time and combat the total support from the political and governmental arena to big business owners and employers. However, this unionism decreased radically at the end of the century, particularly before 1897, because of the increased dislike towards the violent actions carried out by unionists and also because of a series of factors that disfavored workers. One such factor was the increase of mechanization. The second was the lack of protection for workers, which gave employers the power to do whatever they wanted. This changed with the recovery of the economy in 1897, and after this, since the 1900´s unionism began to grow again and empower itself, reaching even the capacity to influence the political and legal arenas. This spike in union organization was best evidenced between World War I and II, when the increase from 1915 and 1920 in the involvement of workers in unions reached its highest peak. What can be said, then, from this graph, and from historical data, is, that between 1900 and 1920, the increment of involvement in labor unions in America more than tripled, compared to the 19th century. This is why the correct answer here is A: Union membership increased more than 5 times between 1900 and 1920.