I understood it quite early in the games. It's one big wiki adventure, a kinda movie you have to watch to understand what's going on. :D

Yah but it's kinda funny how quickly things escalate like it starts out me1 "OMFG IS THAT SAREN HE'S SO -blam!-KING COOL HOLY SHIIIEEET! IS THAT A REAPER?!?! OMG 8=======D" then a couple years later at me3 (planets explode) "eh, we gotta save earth..." Me2 was kind of a middle urgency which I liked and come on, we all liked the suicide mission I always feel so accomplished when people question me and ask how I beat the suicide mission without anyone dying but truth is I just used logic plus I got all the upgrades cuz I figured that they were important

Lol.. I think you need to replay the games a few times to understand what's going on exactly. :D