The Aztecs were the greatest civilization of Mesoamerica. They had cities. They had culture. They were d**n near developing a full writing system. So what if they never had any effect on history? (And oh, did they have an effect...Mexico, despite the Spanish language, is still fundamentally Aztec...And Mexico is 1. the 11th-largest nation in the world by population and 2. a major influence on modern American culture, which in turn is a major influence on world culture) Who are we to say "Well, I think you're a babarian, so you shouldn't be included?"
As for the Vikings: In addition to being the ancestors of the very significant and very civilized Scandinavians (who are none too few on Civfanatics, so beware), they affected history in several ways. First, they conquered a piece of France, and from there, conquered England, and set England on the road that eventually led it to worldwide empire. Second, they rampaged across much of Europe and were a major influence on the policies of most nations in Europe during their formative years in the early Middle Ages; the threat of Viking invasion led to French lords (who were always on the cutting edge of these things) building fortifications that eventually became castles, which in turn meant that the locals were more loyal to their lords than to the king, which in turn led to an institutionalization and entrenchment of feudalism, which in turn led to the entire sorry state of medieval Europe. Third, the Vikings were avid traders and explorers--they were the first Europeans to find America, and they settled Greenland and Iceland. Last, but certainly not least, they founded Russia; looking for trade, they instead became the rulers of local Slavs in Kiev, and eventually led to a unification of Russia.
