The origin of the beat movement can be found with author Jack Kerouac in 1948. The movement itself is considered a counter movement or subculture. The literary works most closely associated with the establishment of the movement are Jack Kerouac's On the Road, William S. Burrough's Naked Lunch, and Allan Ginsberg's poem Howl.
Since it is considered a counter movement we must ask what it reacted against. If we go a little further back in American history the modernist trend reveals itself beginning around the onset of WW I and throughout the interwar period. This, of course, was a global trend that originated in the major urban areas in continental Europe and the US. Modernism with its attempt to peel away tradition has its roots in the years of WW I that left much of the Western World with a profound sense of disillusion. By the end of WW I American intellectuals realized that the military threat was not exclusively the foreign military machine, but the homegrown army as well. In literature this is reflected in such novels as Norman Mailer's The Naked and the Dead and Barbary Shore.
The State was thus increasingly perceived as something that had the power to encroach upon individual freedoms. The beat generation realized this and reacted through writing. It attempted to counter the covert authoritarian state presence and its mainstream values by embracing values that directly countered tradition. In Kerouac's work we thus find open drug use and alcohol abuse, the embrace of America as a geographically limitless space that lends itself to self-discovery through mythical wandering, and the omnipresence of drug use combined with sexual liaisons that have little or no consequences. The latter especially countered traditional family values and would later translate into the free love of the Hippie era. Works of the beat writers, who openly described graphic acts of sexuality, were often deemed obscene in the placid 1950's.
Finally then, the origin of the movement ( and this holds true for most creative movements) can be considered an intellectual reactive impulse rather than a deliberately planned and orchestrated effort. It is important to notice though that even though it is deemed a counter movement and like other counter movements (like political communism in the 1940's or the Hippie counterculture that followed the beatniks) likes to regard itself as subversive and anti-authoritarian, the overarching state that is founded on the principle of participatory democracy, indirectly allows such movements to exist within its boundaries. When we asess its legacy then, we can regard it as a movement that inserted itself into the civic discourse in America at a given point in time.