I feel the reason poker can be traced back to New Orleans is that some say cards, in general, appear to have been popularized in France
and surrounding areas, which New Orleans has a definite link to, (Italy was big too) after being introduced by travelers to/from Asia (China) and northern Africa. These southern Europe areas had a whole mix of games that resembled poker in a sense, but not so much the same betting structure, if any. As the Louisiana Purchase area was being settled (taken by force) by these people in a mixing pot of SE cultures, it took on a whole new structure including a strong gambling aspect.
Poker then moved out west and became a cowboy, popularized by wild stories of people like Wyatt Earp and other 'greats' that would rule the game. As the country evolved and began to settle down a bit, people like Doyle Brunson began to create logistical strategies of the game, and this is where tournament play began to take shape (this was a huge turn of events as tournament play was the catalyst for the poker explosion).
As Vegas started to organize gambling and become the center of the gaming industry, Benny Binion in 1949 arranged the infamous Moss vs. Dandalos heads up match which lasted 5 months. After 21 years of arranging these types of matches, he came up with the idea for the WSOP
with a 6 player tournament. AFter 3 years of this "Main Event" Benny claimed that some day there may be 50 people in the tournament. In 2006 it (currently) maxed out at 8773 thanks predominately to the "Moneymaker Effect". Who knew.
Poker has not settled down as some would speculate, as this years WSOP has the most number of registrants to date (albeit I think they are including rebuys which to me doesnt count), its just spread out more than ever. With online looking like it will become legal across the USA in the next few years, we may see the a new Main Event max coming.