Mostly they affected it through their imperialism. They would colonize and take over countries for resources, and with them they would bring their technologies and things that they needed. After they left these things stayed, things like telephone and telegram lines and similar things. Culturally, they would mostly disregard the local culture and impose their own which would often be accepted and kept by the locals, but often there was also warfare.
Answer: the mosaics in San Vitale differ from the rest of the structures and artworks we have seen because they are all about god being on their side and having imperial might.
They started to trade with others to buy up more land (territories) so eventually they contribute to territory growth
I believe that 1 is the New York area so that would mean the most populated density
Answer:
Japan broke off negotiations as part of their plan to disable and attack the US and its allies in a surprise attack on December 7th, 1941.