Latejoiners are called when they join after the game has started and if u attack for example sparta at turn 1 when it is neutral and a player joins the next turn your units will still attack him but instead of militia sparta will get infantry and a gen if he is premium and after a player latejoins he is automatically peaced with all other players but the very next turn automatically all those peace treaties are ended unless you or he sends you or someone else and ally request
this is to prevent other players insta killing a player that latejoins btw