structural:expansion
History

With the exception of one-pocket, games typically called "pool" today are descended from two English games imported to the United States during the 19th century. The first was English billiards which became American four-ball billiards, essentially the same game but with an extra red object ball to increase scoring opportunities. It was the most popular billiards game in the mid-19th century until dethroned by the carom game straight rail. American four-ball tournaments tried switching to carom tables in the 1870s but this did not save it from being doomed to obscurity; the last professional tournament was held in 1876. Cowboy pool is a surviving member of this group of games.

The second and more influential game was pyramid pool. By 1850 a variant called fifteen-ball pool became popular. Both games were supplanted by continuous pool in 1888, the immediate forerunner of straight pool (1910). New games introduced at the turn of the 20th century include Kelly pool and eight-ball. The distinctive appearance of pool balls with their many colors and division between solid and striped balls came about by 1889. Prior to this, object balls were uniformly deep-red and differentiated only by numbers. English pyramid pool and life pool players were the first to adopt balls with different colors. The stripes were the last addition.