Originally, ales were fermented without hops in cold northern climes. Hops are a preservative and a flavoring and were added later to most beer styles. The sharp, herbal taste of hops is complimentary to the richer, bready flavor of barley.

Nowadays, beer is the generic term; ale is generally used for top-fermented styles common in England and Ireland. Stouts and porters, according to this definition, are ale styles.

Bottom-fermented beers are generally called lagers in distinction, though lager originally meant that the beer had been stored for a time before being drunk. German, East European, American and world-styles are generally lagers. Bock, for instance, is a lager.

Using the definitions above, ales are brewed with top-fermenting yeasts at warmer temperatures and served cool, not cold. Lagers are brewed at colder temperatures with bottom-fermenting yeasts and are served cold.

Then you get into oddities like steam beer and cream ale that reverse one or more of the distinctions between the two main beer styles.

Mass market American beers are all lagers but they also contain as much corn (maize) or rice as they do barley. The warmer climate of most of the US perhaps encouraged such lighter, fizzier drinks developed from German-style brewing. The British, on the other hand, in warmer climates came up with India Pale Ale.

The boutique beers in America, though, may be any style whatsoever and these are popular enough that the big American brewers are trying to get in on the act with a few styles that are more European or British in character.

I used to brew beer and mostly we made ales which are simpler and take less equipment for a home brewer.

Hugs,
Erin