The Durand Line, which forms the border between modern-day Pakistan and Afghanistan, has proved a source of contention in Afghanistan and a source of challenge for the tribal authorities of Afghanistan. The line, which was negotiated between British diplomat and civil servant Mortimer Durand and Afghan Emir Abdur Khan, was a political boundary drawn in 1893 which clearly defined and demarcated the border between Afghanistan and the British Raj. Afghanistan unilaterally disputes the legitimacy of the border. Pashtuns are the prominent ethnic group in eastern Afghanistan and western Pakistan, and the Durand Line served to split their traditional homeland between two nation states. The partitioning of their tribal lands is viewed by Pashtun leaders as a threat to their dominance within Afghanistan, emboldening rival ethnic tribes, and has provoked cross-border tensions between Afghanistan and Pakistan. While having significant political, economic and social impact on Afghanistan, the intervention of the Soviet Union (1979–89), Afghan Civil War (1989–96), Taliban regime (1996–2001) and United States invasion and occupation (2001–present) have not noticeably disrupted the primacy of ethnic tribal authority, and thus the power and influence of warlords, in ordering Afghan society. Although the United States and its coalition allies have expended a considerable amount of time, effort and resources attempting to foment the centralization of government and consolidation of power in the state with its seat of power in Kabul, tribal warlords continue to maintain political influence and power throughout the country outside of Kabul.