Joining AFTER turn 1

Joining after turn 1 has closed means that new players need to wait 3 turns for reinforcements, and that is sometimes all that is needed to tilt the scales.
I suggest giving new joiners reinforcements as though they joined at turn 1, and maybe offsetting the reinforcement by a number from 1 to 3, depending on which turn they joined at.

They already do get more reinforcements though , sometimes a lot more than the country they pick because of the reinf. multiplier because of the other players.