1984 largely hinges around the events of its last book, wherein Winston is taken into the Ministry of Love and systematically tortured and reprogrammed by O'Brien.
Remember the dialogue between O'Brien and Winston in this sequence, as Winston is slowly broken down. The Party is interested solely in domination. There is no ideology (not the kind of ideology that most of history's political movements would adhere to). Instead, they wish only to exert their power over the population and to maintain that power as an end in and of itself.
In that respect, in this last section of the book, I would suggest that Winston embodies all those people the party suppresses (just as O'Brien embodies the Inner Party itself), and those last chapters depict the entire oppressive apparatus of Oceania shown in a microcosm, with Winston himself gradually but systematically broken down. The final breakdown comes when he is brought to Room 101, where O'Brien exploits his fear of rats to force his final capitulation. In fear and terror, he betrays Julia, pleading that she be tortured in his place, and in that act of betrayal, his own last shreds of resistance collapse as well.
Thus, we observe, as Winston's story comes to an end: the complete destruction of a human being.