Zombies, like all pack mobs, call for aid during times of war. When a normal zombie is attacked, all other zombies, as well as any husks and drowned in the area, come to battle alongside their friends. Husks and Drowned, however, only call upon members of their own species to help them fight. Another issue here is that zombies don't retaliate against each other even if you use the actions with commands. Yet if a drowned yeets its trident at a zombie, the zombie will declare war and summon other zombies to battle this drowned. Other drowned don't help the zombie fight the drowned, and when attacked, the drowned will fight back, but other drowned don't help. It's confusing, and I think we need a data tag for zombies and their variants to stop this confusion.