Halo Wars

To unlock all of the timeline events you'll need to collect all the black boxes in campaign mode. If you're only going for the achievement, you won't have to finish each level after you collected the black boxes.

I recommend this site: http://www.xboxlife.com/halo-wars, to find the boxes in campaign, it has photos of the locations (also for sculls).


You'll also have to win each map in skirmish game mode and win a skirmish with each leader.

I recommend these settings:
Players: 1v1; then you don't have to take out two,
Map: All of them; well, duhh :P,
Mode: Deathmatch; Much, much more quicker than Standard,
Difficulty: Easy.

I'd play Capt. Cutter -after you finished playing all leaders- since he has the MAC blast. Build approx. 7-8 warthogs, wait until the MAC blast has charged and attack the enemy base.