Question

when did a news or events become biased

Answer 1

Media bias is the bias or perceived bias of journalists and news producers within the mass media in the selection of events and stories that are reported and how they are covered. The term "media bias" implies a pervasive or widespread bias contravening the standards of journalism, rather than the perspective of an individual journalist or article. The direction and degree of media bias in various countries is widely disputed.
Practical limitations to media neutrality include the inability of journalists to report all available stories and facts, and the requirement that selected facts be linked into a coherent narrative.[1] Government influence, including overt and covert censorship, biases the media in some countries, for example North Korea and Burma.[2] Market forces that result in a biased presentation include the ownership of the news source, concentration of media ownership, the selection of staff, the preferences of an intended audience, and pressure from advertisers.
There are a number of national and international watchdog groups that report on bias in the media.