How do I unlock all the Halo Timeline Events in Halo Wars?

[chris]

I've unlocked all the skulls and found all the black boxes in each mission, but there are still Halo Timeline Events to be unlocked. How do I unlock the rest? Please don't say I have to beat the game on all difficulties

 

[SpinoRap]

Unlock all skulls, get gold on every mission, play on every Skirmish map, unlock all black boxes and use every leader.

 

[Lankey]

Play every single skirmish map, game type and use every single commander