World War II had a profound impact on the game. Beginning late in 1940, baseball saw the impact of the draft, though mildly. In 1941, only 4 major leaguers were called upon. Later, many more men either enlisted or were drafted. By 1945, 509 players from reserve lists and active rosters as well as over 3000 minor leaguers had joined the war effort. Following the war, only 300 of 1000 veterans regained their old playing positions.

In the fall of 1944, Commissioner Landis died and was succeeded by Albert “Happy” Chandler. Chandler was primarily elected in order to answer challenges to the antitrust exemption that had surfaced in the early 1940's.

In the mid-1940's, the Mexican League grew as a rival league for Major League Baseball, threatening to drive player salaries up in order to compete for talent. However, in 1946, Commissioner Chandler ruled that players who jumped to the Mexican League would be barred from MLB for five years. In 1947, Danny Gardella chose to play in the Mexican League without ever being signed by a Major League Baseball team. Upon his return to the United States, he was barred from MLB competition. He filed suit against Major League Baseball. In 1949, Chandler granted amnesty to Mexican League jumpers and Gardella’s case was settled out of court. Due to Major League Baseball’s antitrust exemption, no rival league can be formed in the United States, so MLB is protected from the competition similar to what the Mexican League threatened.

In the spring of 1946, Robert Murphy formed the American Baseball Guild in an attempt to unionize the players. Murphy’s goals included: a $7,500 minimum salary, a formal grievance procedure, reimbursement of player sale prices to the player, pension benefits, the removal of the reserve clause, and increased Spring Training allowances. Murphy attempted to use the Pittsburgh Pirates to begin his union campaign, but the players voted against certifying the union as their bargaining agent and refused Murphy’s advice to go on strike for one game. The Pirates owner had already planned to use replacement players.

Murphy’s union folded after less than a year, but owners formed a study panel to look into the labor situation. The panel became known as the MacPhail Committee. The Major League Executive Council was also created to allow for player input by elected player representatives. The MacPhail Committee agreed to: a 30-day release clause (as opposed to the former 10-day clause), a 25% maximum pay cut, $25 per week as a Spring Training allowance (known as Murphy Money after Robert Murphy), a $500 moving allowance in the event of a trade, a $5,000 minimum salary, and the promise to develop a pension plan.

In February 1947, the players received the first pension plan. The plan covered only five-year veterans and did not cover players already retired. The money for the plan would come from World Series and All-Star Game revenue as well as contributions from owners and players. The plan was for 5 years and was not renewed.

Player salaries for the decade topped out at $100,000, earned by Hank Greenberg in 1947.

In 1949, Commissioner Chandler negotiated the first World Series television contract with Gillette for 6 years at $1 million per year. The contract was then resold to NBC at $4 million per year.