The major hammer throw rule changes in the Olympic era involved the gradual reduction of the field area in which valid throws may land, from a 90-degree angle (i.e., similar to a baseball field's foul lines) down to today's 34.92 degrees, measured from the throwing circle.
In Olympic competition, Irish-Americans dominated hammer throwing in the early 20th Century, then East Europeans won almost all the Olympic gold medals after World War II. But Asia entered the hammer throwing picture when Japan's Koji Murofushi captured the gold in 2004.