Quote Originally Posted by DeltaOne2
AFTER he finishes this, he will click End Turn and the next player will have the option to select his troops & move around. However, if the first player decides that he wants to get involved in a battle, then.. things might get complicated.
There is no reason why all human players cant take their turns all at once. Civ4 works like this.

In a situation where one player needs to fight a battle with another player, It would happen after all players have finished their turn. Then before the next turn starts, uninvolved players would be thrown in a temp chat room while the other two duke it out given a small time period to get it resolved. MOO3 worked like this.