The start of the 20th century might not seem particularly modern–after all, there were only 45 states in the Union, hardly anyone owned a car (the Model T didn’t debut until 1908) and William McKinley, a Civil War vet, occupied the White House. However, 1900 is now considered the beginning of the modern era in Major League Baseball, and today’s records are based on player statistics since that time.
The sport’s pre-modern era encompasses the first official game played in the United States (in Hoboken, New Jersey, in 1846), along with the country’s first professional team, the Cincinnati Red Stockings (whose first season was 1869). Over the course of the sport’s first few decades, however, many of the games’ rules and regulations were in flux, including the distance of the pitcher’s mound from home plate. But by 1900 most of these rules had been codified, and with the founding of the American League and the playing of the first World Series a few years later, baseball became the national pastime we know today.
Baseball experts often divide the modern era itself into variety of periods. For example, 1900 to 1919 is known as the dead ball era, a time when games were low scoring, rules were pitcher-friendly and home runs infrequent. The live ball era, from 1920 to 1945, was noted for higher-scoring games and the rise of Babe Ruth and other power hitters, while the postwar era, which began after World War II and lasted until 1960, was highlighted by Jackie Robinson breaking baseball’s color barrier in 1947. The game’s most recent eras have featured the introduction of divisional play, the advent of free agency and a period from the late 1980s to the late 2000s that has been dubbed the “steroid era,” due to the possibly widespread use of performance-enhancing drugs.