What factors affect the range of a radio transmission?

There is a complex answer to this, so lets put up the basics. First, very low frequency (vlf) radio frequency (rf) energy can "bend" and can travel around the world (literally) as well as penetrate water to some degree. It can be received almost anywhere on the globe. Is that enough range? U.S. Naval submarine communications uses this phenomenon. Electromagnetic radiation (emr) can also travel (propagate) via a "bounce" (can be reflected and/or refracted) off the ionized upper atmosphere (depending on frequency and angle of incidence), and, to a degree, bounce off land and water. It can thereby "bounce" its way around the world. There will be "dead spots" where the signal can't be "seen" by a receiver - unlike a circumnavigating vlf wave. Both those eventualities are power dependent, naturally. The bad news is that if one wants to get a signal from point A to point B, there are variables that will determine what "band" of transmission is best suited to the task.