spoliers
Had to be amolia,,, we all know vic was what started it by killing terry, but amolia really jacked things up for all of them but getting lem in all that trouble.. which dominoed. into he take down..
Their real downfall was putting money before the team. That's when they started fracturing.
Seize the moment, 'cause tomorrow you might be dead.
Their downfall was Shane thinking he could run wild and get in bed with the likes of Antwon Mitchell. This is the reason Lem had to lean on that drug dealer and take the heroin to get intel on the dead girls body.
Also greed was a huge part of it. The money train started the whole Lem not really wanting to be part of it, that led to Shane not really liking/trusting Lem from that point.
But in reality, Vic was the main reason. He put most of this stuff into motion because he always thought he could outsmart everyone.
TWITTER @bigdaddy6666
Have to respectfully disagree with Vic being the main reason. Shane said as much in his suicide note, they all made each other worse, one really wasn't better than the other. Their greed was their downfall. Not Lem burning the money, not Lem taking the heroin to cover Shane, or even Shane getting in bed with Antwon. That was all apart of the domino effect that stemmed from ripping off the money train.
Gilroy foreshadowed it as well in "Coyotes." When he gets tossed in the van and Vic tells him Shane will kill him if he crosses the boarder again, Gilroy says somethinh along the line of "Don't get too greedy Vic, i did, there's a lesson there."
On a side note, i never realized how brilliantly titled the second season finale, "Dominoes Falling," really is until now in hindsight.