 Complete the following phrase:  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 domice 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 197989, Afghan Civil War 198996, Taliban regime 19962001, 2021-present and 