This question hits a bit of a problem of definition. Atheism is variously defined as lack of belief in any deity or as denial of religion. Taking the first definition, some forms of religion like certain forms of Buddhism and some nature religions could be described as atheist, since they don't have deities in the traditional sense.
But if you take atheism in the sense of denial of religion/spirituality altogether, as was the official stance in 20th century communist states like Albania, this did not exist before the industrial age as far as I know. Perhaps on a individual level, but not on a societal level.
The term agnostic is problematic when used on societies. It is really a philosophical position which says "maybe, maybe not". This position can be held towards specific articles of faith, but not towards religion in general. Very few religions are only about belief or non-belief in specific statements. Most religions have ritual, institutions, festivals, traditions etc., and either you partake in that or you don't.