Convergence is a 2015 event that alters the DC Multiverse. The villains Brainiac and Telos took many worlds from their timeline, which allowed many to crossover into each other. This allows DC Comics to revisit bygone eras and stories with a plethora of miniseries tying into the main series, Convergence (Volume 1).
There was an earlier storyline under the same name in 1997, a four issue crossover in several magic-based comic series.
