Newbie Question: What is Upkeep? Anyway to estimate it?

[wc3promet]

What is Upkeep? Anyway to estimate it?

How do I know what is the maximum amount of Army that I can make?

Some player with only 4 cities, killed me with a stack of 40+ Longbowmen, Catapults and Horse Archers.

What early Civics combination was responsible for the above phenomenon?

 

[DwWinnebagos]

where were his cities founded?
Did he conquer others prior to you?

Not enough info to say why. But if it was just one or two stacks, you coul dhave creamed him with cats.