In most modern music in 4/4 beats 2 and 4 are where the snare hits are and are usually referred to as the backbeat. Normally in 4/4 the 2 and 4 beat would not be accented, but the snare hits do just that. Where did this idea originate and why is it so important to accent 2 and 4?
Where did this idea originate? West Africa, then transplanted to the New World. It is a defining characteristic of African-American music, and all the styles of music that grew out of and were influenced by African-American music. It then spread to the rest of the world via the 20th-century music of the USA, Cuba, Brazil, Jamaica, and other nations with African descendants in the population who influenced the musical culture.
Several places I've seen suggest that the "backbeat (accenting beats 2 and 4) originated in the strumming patterns in early country music (then called "hillbilly" to market to "Whites" as opposed to "race" which was marketed to "Blacks" in the 1920s.) Of course, any dance-like 4-beat music has a bit of a metric accent on beats 1 and 3, and syncopation has been around for centuries.
There was (and still is) a lot of cross-influences between genres of music. (Genres are often just marketing.)