"It's as simple as that," Manning told "Nightline" co-anchor Juju Chang in an exclusive interview on "Nightline."
When asked if she felt she owed the American public an apology, Manning said she has accepted responsibility for her actions.
"Anything I've done, it's me. There's no one else," she said. "No one told me to do this. Nobody directed me to do this. This is me. It's on me."
Manning at that time was a 22-year-old Army private named Bradley Manning. The information she disclosed included low level battlefield reports from Iraq and Afghanistan, evidence of civilian deaths in Iraq and Afghanistan, Guantanamo prison camp detainee profiles and U.S. diplomatic correspondence.
In referring to the military documents she was reviewing and what compelled her to risk her career and break the law by leaking them, Manning said, "We're getting all this information from all these different sources and it's just death, destruction, mayhem."
"We're filtering it all through facts, statistics, reports, dates, times, locations, and eventually, you just stop," she continued. "I stopped seeing just statistics and information, and I started seeing people."
Manning said she leaked the documents because she wanted to spark public debate. She said she didn't think leaking them would threaten national security.
"I work with this information every day," Manning said. "I'm the subject matter expert for this stuff. You know, we're the ones who work with it the most. We're the most familiar with it. It's not, you know, it's not a general who writes this stuff."
When asked why she, a low-level analyst, didn't raise her concerns up through the chain of command, Manning said, "the channels are there, but they don't work."
Manning pleaded guilty to some charges and was acquitted of the most serious charge brought against her: aiding the enemy. Her imprisonment was longer than any leaker in U.S. history. President Obama commuted her sentence to time served three days before he left office.
Fighting for hormone treatment was important for her, Manning said, because "it's literally what keeps me alive."
"[It] keeps me from feeling like I'm in the wrong body," she added. "I used to get these horrible feeling like I just wanted to rip my body apart and I don't want to have to go through that experience again. It's really, really awful."
Manning was released from prison on May 17 and has been documenting moments from her daily life on her Instagram and Twitter account, @xychelsea, from taking her first steps out of prison, to playing videos games to hanging out with friends.
Being on the outside, "it's a culture shock for anyone to go through any set of circumstances like that," Manning said.
When asked how she feels about the military today, Manning said, "I have nothing but utmost respect for the military."
"The military is diverse, and large, and it's public, it serves a public function, it serves a public duty," she continued. "And the people who are in the military work very hard, often for not much money, to make their country better and to protect their country. I have nothing but respect for that. And that's why I signed up."
Manning said she hasn't spoken to Obama since he commuted her sentence, but she would want to tell him thank you.
"I've been given a chance," she said. "That's all I asked for was a chance. That's it, and now this is my chance."