UPDS was formed from the March 1999 merger of two terrorist outfits in Assam's Karbi Anglong district, the Karbi National Volunteers (KNV) and the Karbi People’s Front (KPF). The outfit's main area of operations remains the district of Karbi Anglong with a relatively minor presence in the North Cachar Hills district. UPDS has perpetrated several acts of violence with the purported objective of purging the area of non-Karbi settlers including Biharis, Bengalis and Nepalis. The Biharis, who opened the forest areas of Karbi Anglong for sugarcane cultivation in the early fifties, are in a majority in the Hamren sub-division.

The outfit has attempted to exploit the resentment of the tribal Karbi populace against the economic clout enjoyed by the Biharis. In May 2000, the UPDS issued a statement to continue the ‘resistance campaign’ against the environmental, ecological degradation and democratic aggression on Karbi people.

The founder chairman of the outfit, Kiri Rongphar and it’s 'supreme commander', Horen Singh were arrested on October 22, 1999. Presently, the outfit is headed by its 'Chairman' P. Dilli. H. E. Kathar is the General Secretary of the UPDS. The outfit announces its programmes in the name of its 'mass relations secretary' Lt. Leen Timung.

UPDS is reported to have an alliance with other terrorist outfits in the region including the United Liberation Front of Asom (ULFA), Dima Halam Daoga (DHD) and the National Socialist Council of Nagaland-Isak-Muivah (NSCN-IM). In the initial phase, the outfit's cadre were trained and armed by the NSCN-IM. The UPDS, in turn, now acts as the fund collector for the Naga outfit. According to an arrested UPDS leader, 80 per cent of the amount collected through extortion is handed over to the NSCN-IM. The ULFA, which used to have a strong base in the Boithalangchu area of Hamren subdivision, reportedly provided the UPDS insurgents with logistic support.

Extortion remains the main source of funding for the outfit.Williamso Togbi alias Man Singh Togbi is in charge of the extrotion efforts.Government officials and non-Karbi residents of the district are often served with annual tax notices. In some areas, the UPDS has managed to forge an understanding with the village headman (gaonburah), who acts as a middle man in this extortion. Failure to meet the outfit's 'taxes' resulted in the killing of an estimated 20 non-Karbi settlers in March 2000. By June 2000, an estimated two thousand non-Karbi families deserted their villages because of the increasing threat posed by UPDS terrorists.

The outfit which started with an estimated strength of 50 terrorists has procured arms from Bhutan and Bangladesh. Reports suggest that UPDS terrorists now possess sophisticated weapons such as AK-47s, SLRs, US carbines, assault rifles and sophisticated communication devices.The cadre strength has also gone upto 150.The outfit has its 'head camp' in the Disubai area. It also maintains one of its base camp at Bokolia.

According to reports, UPDS cadre is made up of committed terrorists who refrain from ostentatious display of wealth and thus gives them the advantage of easily mingling in the rugged and inaccessible 10,000 square kilometre terrain of the Karbi Anglong district. They carry most provisions with them which helps them to maintain a relative low profile and avoid contact with locals. Thus information on their concentration is hard to come by for security forces to undertake counter-insurgency operations.

Within the Karbi Anglong district, the worst affected region is the Hamren subdivision and Thipu, the district headquarters. Official sources indicate that UPDS terrorists killed 51civilians and 10 security force personnel in 31 incidents in the year 2000. Ten Nepali civilians were killed in two separate attacks on April 19, 2000. On July 16, 2000, 10 non-tribals were killed by UPDS terrorists in two separate attacks at Telihal and Langparban villages. On September 13, 2000, 10 persons including five policemen were killed and four others injured in an ambush by UPDS terrorists in the Barlangphar area. On October 5, 2000 suspected UPDS terrorists killed a police official, his wife and another associate and injured two others at Sexopahar area. Towards the end of year 2000 UPDS again came into focus after perpetrating the massacre of eight non-Assamese settlers on December 28, 2000 in the district. in addition 122 UPDS cadres surrendered in 2000.

News reports have suggested a nexus between some political parties and the UPDS. The outfit has contributed to these speculation by issuing directives to vote for a particular party in the past. Various political parties have accused each other of harbouring UPDS terrorists.

The outfit has suffered several reverses after the October 1999 arrest of its chairman and Supreme Commander. In July 2000, three relatives of the UPDS leaders were killed by unidentified assailants in the Kheroni area of the Hamren subdivision. In August 2000, 25 UPDS terrorists led by the outfit’s secretary S Tarang surrendered at Guwahati.

The government is yet to initiate a dialogue with the outfit. Official sources appear to downplay the threat potential of the outfit particularly in comparison to its more visible counterparts, such as the ULFA, the National Liberation Front of Bodoland (NDFB) and Bodo Liberation Tigers (BLT). Towards the end of 2000, the State government of Assam proposed a ban on the outfit. However, the Indian government is yet to take a decision on this proposal.