ok i'm not positive, but this is what i've picked up...
US Garage came out of new york and got its name from the club "paradise garage" in the 80's. it grew about the same time as "chicago house" was getting bigger, but i believe garage was more like the NYC take on the chicago sound. it tends to be more "shuffly"/percussive and has lots of vocals, but not quite diva house.
this stuff was huge with the black london population. certain dj's began playing the music faster and faster at their weeklies, and it was deemed "speed garage". eventually, after jungle's decline around 96, many producers jumped onto the hot speed garage sound. with the jungle influence the music became synonymous with jump-up style basslines (i've seen armand van helden's remix of spin spin sugar credited as being the first to kickstart this sound, though there is debate). later, rnb producers (mj cole and artful dodger being some of the first i believe) began combining their beats with the 4/4 shuffle of garage, which eventually gave birth to two-step garage. for a while 2-step was almost just a unified genre, but i've read that there is a split happening between the jazzy soulful rnb-influence 2-step and the more breakbeat/jumpup/hard 2-step sounds, similar to the split that happened in the early 90's with breakbeat hardcore.
the moral of the story: 'ardkore ownz j00.
