I often play as the Mongols so early 'Medieval' war is my strategy and I am often at war with 3 civs at once. While getting cities in a peace treaty is possible the AI can often be difficult even when facing complete destruction. I get embargoed, but if you plan for it I can stay in positive gold without having trade routes with CS. A strong military can be useful bullying CS for contributions as well. With a strong military you will overcome much of what the AI can throw at you, I often fall behind in science as well but not too far behind. Flight is an issue, at that point you need to consolidate while you catch up. I don't find war tedious, the terrain is often the biggest challenge. Nothing worse than trying to capture a city with the Great Wall in the middle of a Jungle/Mountain region but it can be done. As regards the diplomatic hits ... "Kill them all and let God sort them out."