playable nations
At the end of the war, Hitler supposedely made a list (according to a WW2 professor of mine) outlining what he believed to be some of the major mistakes of the war. He was angry with Francisco Franco for not joining, and he believed that he missed the boat in the Middle
East. Hitler recognized that the Arab nations under British control in that region had strong nationalistic feelings (+3 rebellion

), and that if he would have interferred in that region, he could have caused a large rebellion that would threaten Britain's control of both that region and North Africa.
It therefore seems extremely important to include other nations that were not involved in the war, for the sole reason that they could have been (and almost were). Of course, there is not much that Columbia could have done (BTW, off the topic, I actually read a book that gave a list of different nations joining WW1 on the allies side, and they had nations like Panama, etc listed for 1917-18, and I thought what the hell did they even contribute to the war effort?), but a nation like Spain or a newly liberated Egypt, could really dampen the Allied war effort.