Nouns can be divided in countable and uncountable. A countable noun means you can count how many there are eg. one car, two steps, five stars etc. Uncountable nouns can't be enumerated eg. orange juice, sand, courage... Uncountable nouns have in most circumstances no plural form. You would not say "two orange juices", but you would say "some orange juice" or "two glasses of orange juice". Apart from some very specific contexts, orange juice never takes a final 's' to show plural. The same goes for 'courage' etc.
When you want to say 'several' or 'a great number' with countable nouns, you use 'many' eg. many cars. If you want to say 'a huge quantity', for uncountable nouns, you use 'much' eg. much orange juice.
Back to our examples: 'enemy' is clearly a countable noun (you can say one, two, one hundred enemies). Thus, "much enemy" is wrong, and "many enemies" is correct.
I pointed out, as a remark, that there's usually no plural after 'much', as (as we saw) uncountable nouns don't have a plural form eg. "much orange juices" is wrong.
Is it clearer?
FRC
