Brostep is a form of dubstep, popularized in the US. It is characterized by its lurching & aggressive wubby bass.
Brostep was popularized by American producer Skrillex. It became extremely popular, and picked up traction in Canada with producers Datsik & Excision. It also attracted the likes of metal bands like Korn, who collaborated with electronic music producers Skrillex & Excision on their album The Path of Totality. By 2016, however, dubstep had declined in popularity, and brostep followed blindly. Artists like Skrillex began working behind the scenes more, producing for trap & pop artists. Mount Kimbie & James Blake began experimenting and making more soulful songs. It didn't help that Datsik was accused of sexual assault in March, leading to cancellation of all of his tour dates and him stepping down from his own label.
Brostep is played at the same tempo as dubstep, 140 (or 70 in a studio). It's characterized by being essentially more hardcore than it's UK counterparts, with heavily distorted bass synths, and lots of wubs. It accentuates the middle negative & uses "robotic fluctuations & metal-esque aggression".