The National Resistance Front of Afghanistan (NRF), also known as the Second Resistance, is a military alliance of former Northern Alliance members and other anti-Taliban fighters loyal to the Islamic Republic of Afghanistan. The founder and president of NRF is Ahmad Massoud. When the Taliban captured Afghanistan on 15 August 2021, former first vice president Amrullah Saleh, citing provisions of the 2004 Constitution, declared himself the caretaker president of Afghanistan and announced the republican resistance against the Taliban. Saleh's claim to the presidency was endorsed by Ahmad Massoud, as well as by former Afghan Minister of Defence Bismillah Mohammadi, and the Afghan embassy in Tajikistan including its ambassador Mohammad Zahir Aghbar.

The Northern Alliance, officially known as the United Islamic National Front for the Salvation of Afghanistan, was a military alliance of groups that operated between early 1992 and 2001 following the dissolution of the Soviet Union. At that time, many non-Pashtun Northerners originally with the Republic of Afghanistan led by Mohammad Najibullah became disaffected with Pashtun Khalqist Afghan Army officers holding control over non-Pashtun militias in the North. Defectors such as Rashid Dostum and Abdul Momim allied with Ahmad Shah Massoud and Ali Mazari forming the Northern Alliance. The alliance's capture of Mazar-i-Sharif and more importantly the supplies kept there crippled the Afghan military and began the end of Najibullah's government. Following the collapse of Najibullah's government the Alliance would fall with a Second Civil War breaking out however following the Islamic Emirate of Afghanistan's (Taliban) takeover of Kabul, The United Front was reassembled.