The US Army intelligence analyst, who is half British and went to school in Wales, appeared to sink into depression after a relationship break-up, saying he didn't "have anything left" and was "beyond frustrated".In an apparent swipe at the army, he also wrote: "Bradley Manning is not a piece of equipment," and quoted a joke about "military intelligence" being an oxymoron.
Mr Manning, 22, who is currently awaiting court martial, is suspected of leaking more than 90,000 secret military documents to the Wikileaks website in a security breach which US officials claim has endangered the lives of serving soldiers and Afghan informers.
Supporters claim the war logs leak exposed civilian deaths in Afghanistan which had been covered up by the military, and Mr Manning's family, who live in Pembrokeshire, said he had "done the right thing".
The Pentagon, which is investigating the source of the leak, is expected to study Mr Manning's background to ascertain if they missed any warnings when he applied to join the US Army. The postings on his Facebook page are also likely to form part of the inquiry.
Mr Manning, who is openly homosexual, began his gloomy postings on January 12, saying: "Bradley Manning didn't want this fight. Too much to lose, too fast."
At the beginning of May, when he was serving at a US military base near Baghdad, he changed his status to: "Bradley Manning is now left with the sinking feeling that he doesn't have anything left."
Five days later he said he was "livid" after being "lectured by ex-boyfriend", then later the same day said he was "not a piece of equipment" and was "beyond frustrated with people and society at large".
His tagline on his personal page reads: "Take me for who I am, or face the consequences!"
Mr Manning was arrested at the end of May on suspicion of leaking a video of a US helicopter attack, and quickly became the main suspect when the Afghan war documents were leaked earlier this week.
His uncle, Kevin Fox, said the soldier's arrest and imprisonment in a military jail had taken its toll on his mother Susan, who lives in Haverfordwest.
"She hasn't been well," he said, adding that if Mr Manning had leaked the documents: "I think the boy did the right thing."
Another close relative, who asked not to be named, said: "His mum didn't know anything about what he was doing and it's come as a big shock. She's very upset."
Susan Manning, 56, moved to the US in 1979 after marrying Bradley's American father Brian Manning, a former serviceman who was based at the Cawdor Barracks in Brawdy, near Haverfordwest.
Bradley Manning was born in Oklahoma but the couple divorced in 2001 and Mrs Manning moved back to Wales with her son, who sat his GCSEs at the Tasker Milward secondary school in Haverfordwest.