The dirty little secret to this game is that the AI is bad at war and using their units in general, so there is no reason to fear their military outnumbering you. The case with Arabs attacking him early on was the classic scenario of what I'm talking about. Even at Diety level, there is just no reason to be scared of that situation; you can turtle out of it in a few turns, then turn the tide and go on the march, as long as you have basic defense and some production or gold to turn out units later on. Once you learn this trick, i.e., that the AI is usually never going to actually capture your cities (unless you do something really silly) your results will improve dramatically. You pick off the AI's units, wait it out, then take them down. And even in better in this situation was that they attacked him first so he didn't get the diplo penalty.