Nippon Professional Baseball, or NPB, is the highest level of baseball in Japan. Outside Japan, it is often just referred to as "Japanese baseball". The roots of the league can be traced back to the formation of the "Greater Japan Tokyo Baseball Club" in Tokyo, founded 1934 and the original circuit for the sport in the Empire two years later - Japanese Baseball League (1936-1949), and you can see that they continued to play through the dark years of total warfare.

The new NPB for Japan was formed when that sports organization reorganized in 1950, with the combination of its two leagues with six teams each of the Central League and the Pacific League. The annual season ends with the Japan Series championship play-off series of games starting that year for the JPB being modelled along the lines of the American World Series tournament.

More Info: en.wikipedia.org