Moonsinger said:
No offense, but I think you guys are wrong about that. It really isn't about the size of your military but quality of your military that matters. Sure, bigger size always has an advantage, but quality must come first.

For example, if your next door neighbor has 25 chariots, just build one spearman and he will think twice before picking on you. Why? By deductive reasonning, he knows that if you can build one spearman, you surely have the ability to build more spearmans. If he attacks, you may pop-rush more spears and he will be dead. It would be best to go pick on someone else who have no spears.
Of course, there are other factors but size isn't one of them. Why? Becuase if size does really matter, then none of us would have any chance on beating the deity level where the AIs always have bigger guns and everything else.
PS: For some reasons, I feel so dirty talking about this. I'm going to take a fresh shower and go to bed now. Bye...
I'm not completely sure about this, but...
My understanding (and experience) is that if you are low on the power graph, you are a target. I seriously doubt the AI looks at individual units (e.g. one spearman) and makes decisions based on that. It is simply not that sophisticated.
However, it is important to keep in mind that the power graph is not determined solely by how many military units you have. Your tech position is also factored in. So, you can have a high power rating based on the fact you are 5 techs ahead of your nearest competitor, without necessarily having a large number of military units. I've read in other threads that the tech part of the power rating is determined by military techs, but I'm not sure that is correct. In any case, if you are ahead in tech, you are probably (note I say probably) ahead in military tech as well.
By watching my power rating carefully, I've observed my power rating go up as I build military units. It goes up more when you build more powerful (for the era) units. It's my belief that if you are the first to build a particular unit (e.g. maceman) then that unit is given much more weight in determining your power rating than other units. It makes sense, although I can't claim I'm 100% sure about it. Still, if my power rating needs some help, I am careful to always build a unit based on a newly researched tech whether I really want or like that unit. A perfect example: I usually build one musketman, even though I'm not particulary fond of them.
Given the above, it's just as important, or maybe more important, to be competitive or ahead in tech if you want to keep your power rating up. If you have to keep your power rating up by building lots of military units (because you are behind in tech), then unit support costs bog down your economy even more, and you can fall more behind in tech. Not good.
Another aspect: Just because you have a high power rating doesn't necessarily mean your military is the strongest. If your high power rating is based on your tech lead, your military could be relatively weak. The flip side is you can't assume a Civ with a low power rating doesn't have many military units.
I don't often see it discussed on the forum, but I believe that your economy is your greatest military asset. It keeps you in the tech race, which keeps your power rating up, which puts you in the driver's seat for the wars you are involved in. If no one will declare war on you because of your power rating, then your only wars are the ones you choose.