In this game you are given various tasks to complete and a preset-sized army to get the job done with. In between each of the missions that you have, you will have a chance to restock with more battle fodder. In addition you get to level in a style very similar to what you would expect from an RPG, so even if your army stays the same size, you can still increase your strength. Then again, since Battle March is an expansion from the Mark of Chaos, the fact that it follows that format is no surprise at all.
Of course this expansions claim to fame is the edition of the green peoples and the dark ones. In less poetic terms that means orcs and goblins for the green skins and dark elves.
In this expansion pack you get into the big green shoes of the Ork Gorbash and you begin your preparations for war. As you may have guessed, the Orks are not running the show themselves - they are being coerced and manipulated by the Dark Elves. I can safely tell you without spoiling too much of the plot that you will be helping the Dark Elves with their most evil of plans. Their end goal is nothing less then genocide. On the bright side you will also be playing some time as a Dark Elf.