Keep your forces home until your base is defendable as always. Build up your great hall to a fortress and get the structures you're lacking all the while purchasing unit upgrades. Attacks here will come from the northeast, northwest and east. And the chaos orcs aren't pushovers. They can take down buildings fast so watch towers are only really useful for softening and slowing the enemy. You must keep a force defending your base! It will not be too long before a cutscene reveals burning infernals crashing from the sky! They're assaulting your base right when it's over too so prepare to fight. When things are under control take your attack force (I recommend leaving Cairne at home to help defend! Otherwise take Thrall, two tauren, four grunts, three witch doctors and two kodo beasts at least!) to the east. Deal with the thunder lizards here to find a potion of healing which is probably useless to you. Anyway, head further east and fight the large group of harpies you find here. Inside the eastern hut you'll discover a scroll of mana. Now let's fight some Orcs.

Northwest of the harpies you'll see the first of many small orc outposts you can eliminate to cut back on the resistance. There is nothing very challenging about this one, so it was a good place to start. There is a goblin laboratory they were guarding. You could use the reveal ability at the expense of some gold but Thrall's far sight ability is probably far more efficient now as you are probably nearing level 10 and may even have it at the highest level. You can use it to reveal the entire map if you like. Thrall should regenerate mana very quickly at this point. Anyway, head to the northeast and eliminate the orc you see guarding the gold mine. You may need it later if yours runs out. When I attacked this location two infernals dropped from the sky. This will probably happen to you, too.

I had a burning desire to wipe all the orcs off the map at this point. Northeast of your base there is another gold mine. Use the far sight ability and you'll see that there are some orc forces there. Take Thrall's attack force and eliminate them. My forces were attacked by another infernal here. I headed northeast toward the fountain of health. There are a group of centaurs there who drop a scroll of protection and a mask of death (vampiric attack). Go northeast and take out the small orcish base there. Start from the east and work your way west. Things should be pretty much under control now and you can replenish your attack force and move on from danger to danger. Now only one base stands between your forces and Grom Hellscream. It's the one to the northeast of your current location. This is more challenging than the last. I know they're the same side and the same base technically but the one before was quite detached and poorly defended. When you manage to eliminate the base here you can't just march right on to Grom (who is almost at the northeast corner of the map) as there are lots of defenders. You must get past some of the worst units the legion has to offer but still, it's not undoable as the doom guards aren't immune to magic like the infernals. When you DO get to Grom simply click the soul gem then click on grom to use it on him. You don't even have to fight him. You will have to eliminate those doom guards but they're nothing alone. Now take the soul gem to Jaina's Circle, which is to the west of your base.