The development of poker is linked to the historical movement that also saw the invention of commercial gambling. English actor Joseph Cowell reported that the game was played in New Orleans in 1829, with a deck of 20 cards, and four players betting on which player's hand was the most valuable. Jonathan H. Green's book, An Exposure of the Arts and Miseries of Gambling (G. B. Zieber, Philadelphia, 1843), described the spread of the game from there to the rest of the country by Mississippi riverboats, on which gambling was a common pastime. As it spread north along the Mississippi River and to the West during the gold rush, it is thought to have become a part of the frontier pioneer ethos.

Source: Wikipedia