That article says 1816 was the year for the first steamship to go out to sea but in a post further up which is a quote from the devs, they stated something about Waterloo being past the time frame of the game, that battle if I'm not mistaken was 1815.

So....we need more info, lol.
In Empire if you want you can research tech from slightly beyond the time frame covered by the game if you put the effort into it. So that's why you might see Steam ships in the campaign.

And America will be playable.