MGS4: It is 2014, 9 years after the Shadow Moses incident, 7 years since Big Shell. War has changed. War has become routine, no longer about politics or ideologies, just to become the best in the war economy. Nanomachines in soldiers bodies make everything controlled. Emotional control, equipment control, physical control, everything. It is all monitored in the SoP, Sons of the Patriots, system. PMC's, Private Military Companies, are constantly starting wars. 3 days before he is sent to South America to aid the rebels in the area, Solid Snake, AKA Old Snake, due to accelerated aging in his genetic code, is forced out of retirement. Colonel Cambell alerts Snake that Liquid Ocelot, Revolver Ocelot's body taken over by Liquid Snake after having his arm cut off by Grey Fox in MGS1 and taking Liquids arm, his will soon being taken over, that he is there. Snake goes to SA and figures out he is trying to take over the SoP system and rebuild Big Boss' dream: Outer Haven, a world free of Patriot control.
Just ask if you wish to hear more, or find some gameplay from Youtube.