The distinct evolution of baseball from among the various bat-and-ball games is difficult to trace with precision. While there has been general agreement that modern baseball is a North American development from the older game rounders , the 2006 book Baseball Before We Knew It: A Search for the Roots of the Game , by David Block, argues against that notion. [1] The earliest known mention of the sport is in a 1744 British publication, A Little Pretty Pocket-Book , by John Newbery. It contains a wood-cut illustration of boys playing "base-ball," showing a set-up roughly similar to the modern game, and a rhymed description of the sport. The earliest known American reference to the game was published in a 1791 Pittsfield, Massachusetts , statute that prohibited the playing of baseball within 80 yards of the town's new meeting house. The English novelist Jane Austen made a reference to children playing "base-ball" on a village green in her book Northanger Abbey , which was written between 1798 and 1803 (though not published until 1818).

The first full documentation of a baseball game in North America is Dr. Adam Ford's contemporary description of a game that took place in 1838 on June 4 (Militia Muster Day) in Beachville, Ontario; this report was related in an 1886 edition of Sporting Life magazine in a letter by former St. Marys, Ontario , resident Dr. Matthew Harris. In 1845, Alexander Cartwright of New York City led the codification of an early list of rules (the so-called Knickerbocker Rules ), from which today's have evolved. While there are reports of Cartwright's club, the New York Knickerbockers , playing games in 1845, the game now recognized as the first in U.S. history to be officially recorded took place on June 19 , 1846 , in Hoboken, New Jersey , with the "New York Nine" defeating the Knickerbockers, 23–1, in four innings.

Semiprofessional baseball started in the United States in the 1860s; in 1869, the first fully professional baseball club, the Cincinnati Red Stockings , was formed and went undefeated against a schedule of semipro and amateur teams. By the following decade, American newspapers were referring to baseball as the "National Pastime" or "National Game." The first "major league" was the National Association , which lasted from 1871 to 1875. The National League , which still exists today, was founded in 1876. Several other major leagues formed and failed, but the American League , established in 1901 as a major league and originating from the minor Western League (1893), succeeded. While the two leagues were rivals who actively fought for the best players, often disregarding one another's contracts and engaging in bitter legal disputes, a modicum of peace was established in 1903, and the World Series was inaugurated that fall. The next year, however, the National League champion New York Giants did not participate as their manager, John McGraw , refused to recognize the major league status of the American League and its champion, the Boston Americans . The following year, McGraw relented and the Giants played the Philadelphia Athletics in the World Series.

Compared with the present day, games in the early part of the 20th century were lower scoring and pitchers were more successful. The "inside game", whose nature was to "scratch for runs", was played rather more violently and aggressively than it is today. Ty Cobb said of his era especially, "Baseball is something like a war!" This period, which has since become known as the " dead-ball era ", ended in the 1920s with several rule changes that gave advantages to hitters and the rise of the legendary baseball player Babe Ruth , who showed the world what power hitting could produce and thus changed the nature of the game. Two of the changes introduced were a move to bring the outfield fences closer to the infield in the largest parks, and an introduction of extremely strict rules governing the size, shape and construction of the ball, causing it to travel farther when hit; the aggregate result of these two changes was to enable batters to hit many more home runs.

In 1884, African American Moses Walker (and, briefly, his brother Welday) had played for the Toledo Blue Stockings of the major-league-level American Association . An injury ended Walker's major league career, and by the early 1890s, a "gentlemen's agreement" in the form of the baseball color line effectively barred African-American players from the majors and their affiliated minor leagues, resulting in the formation of several Negro Leagues . The first crack in the agreement occurred in 1946, when Jackie Robinson was signed by the National League's Brooklyn Dodgers and began playing for their minor league team in Montreal. Finally, in 1947 , the major leagues' color barrier was broken when Robinson debuted with the Dodgers. Although the transformation was not instantaneous, baseball has since become fully integrated .

Major League baseball finally made it to the West Coast of the United States in 1958, when the Brooklyn Dodgers and New York Giants relocated to Los Angeles and San Francisco respectively. The first American League team on the West Coast was the Los Angeles Angels , who were founded as an expansion team in 1961.

Pitchers dominated the game in the 1960s and early 1970s. In the early 1970s the designated hitter (DH) rule was proposed. The American League adopted this rule in 1973, though pitchers still bat for themselves in the National League to this day. The DH rule now constitutes the primary difference between the two leagues.

Despite the popularity of baseball, and the attendant high salaries relative to those of average Americans, the players have become dissatisfied from time to time, as they believed the owners had too much control and retained an unfair share of the money. Various job actions have occurred throughout the game's history. Players on specific teams occasionally attempted strikes, but usually came back when their jobs were sufficiently threatened. The throwing of the 1919 World Series , the " Black Sox scandal ", was in some sense a "strike" or at least a rebellion by the ballplayers against a perceived stingy owner. But the strict rules of baseball contracts tended to keep the players "in line" in general.

This began to change in 1966 when former United Steelworkers chief economist (and assistant to the president) Marvin Miller became the Baseball Players Union executive director. The union became much stronger than it had been previously, especially when the reserve clause was effectively nullified in the mid-1970s. Conflicts between owners and the players' union led to major work stoppages in 1972, 1981, and 1994. The 1994 baseball strike led to the cancellation of the World Series, and was not settled until the spring of 1995. During this period, as well, many of the functions — such as player discipline and umpire supervision — and regulations that had been administered separately by the two major leagues' administrations were united under the rubric of Major League Baseball .

On a happier note, 1995 was the year Cal Ripken, Jr. played in his 2,131st consecutive game, breaking Lou Gehrig 's record. The number of home runs increased dramatically after the strike. Mark McGwire and Sammy Sosa both shattered Roger Maris 's long-standing single season home run record in the late 1990s. In 2001, Barry Bonds established the current record of 73 home runs in a single season. Bonds has also gone on to hit more homers in his career than any player other than Henry Aaron . Even though all three sluggers have been accused in the steroid -abuse scandal of the mid-2000s, their feats did do a lot at the time to bolster the game's renewed popularity.