Modern Warfare 2 - Part 1
2016: This is where things start to get a little bit complicated.
Shepherd recruits Army Ranger Joseph Allen for a top secret assignment. Allen is given a new identity and sent undercover to infiltrate Makarov's terrorist outfit, which he manages to do. The thing is, Shepherd actually wants Allen to fail in this mission, and secretly ensures that he'll be found out by leaking information to Makarov. It's not clear whether he does this indirectly, or if the two men are knowingly working together despite being enemies.
Two members of Task Force 141 - Captain MacTavish and Sergeant Gary "Roach" Sanderson - are despatched to a Russian airbase in the Tian Shan mountains. They have been sent to recapture an ACS module - a highly sensitive bit of kit that was aboard a satellite that crashed. The module itself plays a crucial role in maintaining the United States ' defense grid. MacTavish and Roach succeed in recapturing the module; unfortunately the Russians have already copied the information they needed from the device, but no-one knows this yet.
Makarov and his men launch a horrific attack on Zakhaev International Airport, massacring countless civilians. Crucially, the terrorists keep their identity a secret, remaining silent throughout so that their nationality can't be confirmed. Just as the gang are about to escape, Makarov unexpectedly shoots and kills Allen. When the authorities close in, they find his body and realise he's an American. The Ultranationalists declare war on the USA, and the poop hits the fan.
Here's the kicker, though: Shepherd planned for all this. He set up Allen to fail in his assignment, he (presumably) arranged for the ACS satellite to be brought down. Why? Because if the Russians start World War III and invade the USA, thousands of people will join the military, and he'll be in charge of a massive force that will allow him to get some payback for the events of CoD 4. Or as Shepherd puts it himself, towards the end of the game:
"Five years ago I lost 30,000 men in the blink of an eye - and the world just f***ing watched. Tomorrow there will be no shortage of volunteers, no shortage of patriots."
There are a number of logistical problems with Shepherd's plan. How did he arrange for the satellite to crash, and in exactly the right place? If he wants the Russians to have the ACS module, why did he send Soap and Roach to get it back? It seems unlikely that Shepherd and Makarov would directly collaborate, but if this wasn't the case then how did Shepherd know that Allen would be killed and framed at exactly the right moment?
Beyond this, it seems weird that Shepherd wants to do this in the first place. He's already powerful, for a start - and by helping the Russians to invade he's actually weakening his own side, not to mention the American economy. And if it's all revenge for what happened five years ago, why is he helping Makarov, who was Zhakhaev's buddy? It's like two football firms agreeing to organise a brawl after a match, only on an international level.
The real answer to all these questions: because it's a video game, that's why.