Ted Halson - Historian of the Halo Wars
"You are being lied to."
This was the opening of Robert Watts' famous Covenant warning, often called the Cassandra speech. Robert Watts publically warned the people of the outer colonies that an alien force, now known as the Covenant, was planning to attack. He warned them that they planned on inflicting a total war on humanity, a war of genocide, and claimed that the UNSC knew about it. He warned that the USNC was planning to allow the outer colonies to be murdered, using them as ablative armor for the inner colonies and removing their ability to determine their own futures.
He warned the people of the outer colonies that they had 9 months to prepare, 9 months to get to safety or train or make peace with their maker. The Front was working on countermeasures but the people of the outer colonies would have to work together, would have to help themselves, because the UNSC was not going to give them meaningful help.
The UNSC denied this claim, they said that Robert Watts had gone crazy and claimed this was just proof that the insurrectionist movement was made of deranged madmen. This propaganda campaign worked, to a degree. Recruitment into the United Rebel Front went down and other rebel groups grew during this period. It seemed at the time that the Front had spent quite a bit of their goodwill to make crazy claims.
Then the attacks started. The war started and the UNSC, having spent so much political capital smearing the Front, could not afford to let the news out but quickly ran into a wall. It's kind of hard to cover up an alien invasion, especially when you're losing. So colonies went dark, the news got out and, amongst many in the outer colonies, there was the feeling that the Front had been right all along.
It probably would have just been a footnote in history if the Front did not have the legendary doctor Monk on their side. The UNSC after all controlled most of the industry and had the only navy worth the name. Whatever Watts said people would have turned to the UNSC for protection, out of desperation and lack of a credible alternative.
The rebel fleet however changed that calculation by quite a bit.