According to local tradition in the early times of the Karenni states there was a principality led by a "Sawphya" that was under the over lordship of a Shan prince.

After the death of this prince in 1869 his two sons renewed the petition claiming that they feared Burmese ambitions on their state.

On 27 May 1942, during World War II, nearby Kengtung State was invaded and its capital captured by the Thai Phayap Army.

In 1992, it appointed Róbert Cey-Bert as its international ambassador, whose diplomatic efforts[7][8] led to the KNU's admission to the Unrepresented Nations and Peoples Organization (UNPO) in 1993.

Resources like the hydropower and mining led to massive military presence around the state; thus, leading many of its people without a home and more problems to arise.

[10] The armed conflict did not end there, however, with the KNU's new headquarters being established in Mu Aye Pu, on the Burma-Thai border.

In 2004, the BBC, citing aid agencies, estimated that up to 200,000 Karen, including Karenni, had been displaced during the decades-long war, with a further 160,000 living in refugee camps on the Thai side of the border.

[11] In February 2010, reports said the Burmese army was continuously burning Karen villages, displacing thousands of people.

[3] More than half of its territory was located east of the Salween River, an area that was annexed by Thailand during World War II.