Playing as the Empire, raze the Dwarfs' capital at Karaz-a-Karak.
The steam tank requires a high tier building to recruit so it may take you time, but it's not difficult to get to at all. Playing as the Empire, recruit a Steam Tank to one of your armies. Put 10 in the same army for the achievement. The Reiksguard will probably be your mainstay cavalry unit for a while in your campaign so getting 10 of them recruited won't be a problem.
Playing as the Empire, have at least 10 Reiksguard units in a single army. This must be fought out on the battle map, not autoresolved. This can be a combination of Lords and Heroes, it doesn't have to be three of one type. Playing as the Empire, win a campaign land battle with three or more Lords and Heroes in your army.
