Prohibition was actually the result of a long fight on the part of reformers and organizers to see alcohol banned, reaching back into the 1800s with the Temperance Movement. Indeed, long before alcohol was banned nationwide, local pressure had already seen it banned throughout the country on a state level. Note that, in its time, Prohibition was seen and referred to as the "noble experiment," a phrasing that tells us much about how the policy was actually viewed and understood among its supporters.
One thing you should remember is the influence of religion in shaping much of American history, and the great reform movements of the early 1800s, Temperance among them, were no different in this respect. Influenced by religious conviction, Temperance became a moral stand by which alcohol was associated with social ills and criminality, and an evil to be purged from United States society.
At the same time, however, it is important to remember the context of life in the nineteenth century, and the conditions these reformers and organizers were working against. It is also important to remember that many of their leaders were women, and this was not by accident. In truth, people in the early nineteenth century tended to, on average, drink a great deal more than people drink today, and this high rate of drunkenness also led to high rates of domestic violence and abuse. In this sense, the desire to ban alcohol, for many women, had a very self-protective component (and this was in a world where women lacked many of the legal and social protections they have today, most of which have only been gained in the twentieth century).
At the same time, even as reformers might have termed prohibition along the lines of the "noble experiment," there were also far less noble influences at work. Xenophobia played a hand in this as well, with alcohol particularly associated with the immigrant communities Americans were so often hostile against, and in this sense, Prohibition (along with the larger Temperance Movement preceding it) seems to have gone hand in hand with the nativist waves sweeping across the country.
To conclude, I would say the most important feature to be aware of regarding Prohibition is this: it was not a sudden turning point or new development that emerged in the early twentieth century but was rather the culmination of much deeper groundswells that had already been present for a very long time.