Drake and Kendrick Lamar beef explained - what has happened and why?

Rappers have been trading insults since the dawn of hip-hop. It's part of the culture. A test of lyrical skill and a declaration of superiority that has produced hundreds of classic "diss tracks", from 2Pac's Hit 'Em Up to Jay-Z's Takeover. The latest beef originally erupted between three of hip-hop's biggest stars - Drake, Kendrick Lamar and J Cole - all triggered by a seemingly innocuous lyric praising their respective careers. As tensions grew, Cole dropped out of the fight. However, Drake and Kendrick continue to battle with increasing ferocity - levelling life-changing accusations against each other in a flurry of tracks. Here's a guide to the battle's history, its fire starters, flashpoints and future.