The information is said to include 250,000 US diplomatic messages and footage of two airstrikes.
One video filmed in July 2007, in Baghdad, reportedly shows a US helicopter attack on a group of men, including two journalists. The other video was filmed in May 2009 in Granai, Afghanistan.
Manning was working at a US base near Baghdad. His job as an intelligence analyst gave him access to a restricted computer network used by the military to send classified information.
During online chats he allegedly admitted downloading the materials. He has been charged with more than 20 offences, including leaking two videos and more than 500,000 documents, and illegally passing on classified defence information to post on the internet.
Some people believe the alleged crimes shown in the WikiLeaks documents outweigh any crime Manning might have committed.
It is wrong he is being punished while people committing war crimes and human rights abuses are not investigated and prosecuted. I think if Manning really did this, then it was heroic to stand up for what he thought was morally right.