The United People's Democratic Solidarity (UPDS) was formed in March 1999 with the merger of two militant outfits in Assam's Karbi Anglong district — the Karbi National Volunteers (KNV) and Karbi People's Front (KPF).

UPDS signed a ceasefire agreement for one year with the Union Government on May 23, 2002. This led to a split in UPDS with one faction deciding to continue with its subversive activities while the other commenced negotiations with the government. Currently, there are two factions: pro-talks and anti-talks. On May 16, 2004, the anti-talks faction of UPDS rechristened itself as the Karbi Longri North Cachar Hills Liberation Front (KLNLF) and its armed wing as the Karbi Longri North Cachar Hills Resistance Force (KNPR).

Both the founder 'chairman' of the outfit, Kiri Rongphar, and its 'supreme commander', Horen Singh, were arrested on October 22, 1999. On August 22, 2002, UPDS 'commander-in-chief' Long Kumar Kiling died of injuries suffered during a feline attack in the forests of Karbi Anglong district. The cadre strength of UPDS is estimated to be a little more than 150 (including both factions), out of which at least 50 are believed to be armed with sophisticated weapons. Its main area of operations is in Karbi Anglong district, with a relatively minor presence in North Cachar Hills district.

On January 17, 2006, UPDS decided to drop its main demand for an autonomous state and instead settled for additional powers to the existing autonomous council.