The Islamic Republic of Afghanistan was a presidential republic in Afghanistan from 2004 to 2021. The state was established to replace the Afghan interim (2001–2002) and transitional (2002–2004) administrations, which were formed after the 2001 United States invasion of Afghanistan that had toppled the partially recognized Taliban-ruled Islamic Emirate of Afghanistan. However, on 15 August 2021, the country was recaptured by the Taliban, which marked the end of the 2001–2021 war, the longest war in US history. This led to the overthrow of the Islamic Republic, led by President Ashraf Ghani, and the reinstatement of the Islamic Emirate under the control of the Taliban, today the ruling government of Afghanistan. While the United Nations still recognizes the Islamic Republic as the legitimate government of Afghanistan, this toppled government controls no portion of the country. The US–Taliban deal, signed on 29 February 2020 in Qatar, was one of the critical events that caused the collapse of the Afghan National Security Forces (ANSF). Following the deal, the US dramatically reduced the number of air attacks and deprived the ANSF of a critical edge in fighting the Taliban insurgency, leading to the Taliban takeover of Kabul.

Following the September 11 attacks, the United States and several allies invaded Afghanistan, overthrowing the Taliban's first government (which had limited recognition) in support of the opposition Northern Alliance. Afterwards, a transitional government was formed under the leadership of Hamid Karzai. After the 2003 loya jirga, a unitary presidential Islamic republic was proclaimed under a new constitution, and Karzai was elected for a full term as president. Meanwhile, the US-led international coalition helped maintain internal security, gradually transferring the burden of defense to the Afghan Armed Forces after 2013–14.

However, Taliban forces held control of various areas of the country and the civil war continued. The Taliban regrouped as an insurgency with the alleged support of Pakistan, and escalated attacks on Afghan and coalition forces after 2006–07. This perpetuated Afghanistan's problematic human rights and women's rights records, with numerous abuses committed by both sides, such as the killing of civilians, kidnapping, and torture. Due to the government's extensive reliance on American military and economic aid, some classed the nation as an American client state, and it gradually lost control of the rural countryside after the conclusion of Operation Enduring Freedom.

During the withdrawal of NATO troops in 2021, the Taliban launched a massive military offensive in May 2021, allowing them to take control of the country over the following three and a half months. The Afghan National Army rapidly disintegrated. The institutions of the republic effectively collapsed on 15 August 2021, when the Taliban forces entered Kabul and Afghan president Ashraf Ghani fled the country. Soon after, former first vice president Amrullah Saleh declared himself the caretaker president of Afghanistan and announced the republican resistance against the Taliban; however, on 6 September 2021, Saleh also fled to Tajikistan.

In December 2001, after the Taliban government was overthrown, the Afghan Interim Administration under Hamid Karzai was formed. The International Security Assistance Force (ISAF) was established by the UN Security Council to help assist the Karzai administration and provide basic security. By this time, after two decades of war as well as an acute famine at the time, Afghanistan had one of the highest infant and child mortality rates in the world, the lowest life expectancy, much of the population were hungry, and infrastructure was in ruins. Many foreign donors started providing aid and assistance to rebuild the war-torn country.

Taliban forces meanwhile began regrouping inside Pakistan, while more coalition troops entered Afghanistan to help the rebuilding process. The Taliban began an insurgency to regain control of Afghanistan. Over the next decade, ISAF and Afghan troops led many offensives against the Taliban, but failed to fully defeat them. Afghanistan remained one of the poorest countries in the world because of reliance on subsistence agriculture, a lack of foreign investment, government corruption, and the Taliban insurgency. Meanwhile, Karzai attempted to unite the peoples of the country, and the Afghan government was able to build some democratic structures, adopting a constitution in 2004 with the name Islamic Republic of Afghanistan. Attempts were made, often with the support of foreign donor countries, to improve the country's economy, healthcare, education, transport, and agriculture in Reconstruction in Afghanistan. ISAF forces also began to train the Afghan National Security Forces. Following 2002, nearly five million Afghans were repatriated. The number of NATO troops present in Afghanistan peaked at 140,000 in 2011, dropping to about 16,000 in 2018.

In September 2014, Ashraf Ghani became president after the 2014 presidential election where for the first time in Afghanistan's history power was democratically transferred. On 28 December 2014, NATO formally ended ISAF combat operations in Afghanistan and transferred full security responsibility to the Afghan government. The NATO-led Operation Resolute Support was formed the same day as a successor to ISAF. Thousands of NATO troops remained in the country to train and advise Afghan government forces and continue their fight against the Taliban. It was estimated in 2015 that "about 147,000 people have been killed in the Afghanistan war since 2001. More than 38,000 of those killed have been civilians." A report titled Body Count concluded that 106,000–170,000 civilians have been killed as a result of the fighting in Afghanistan at the hands of all parties to the conflict.

On 14 April 2021, NATO Secretary General Jens Stoltenberg said the alliance had agreed to start withdrawing its troops from Afghanistan by 1 May. Soon after the withdrawal of NATO troops started, the Taliban launched an offensive against the Afghan government, quickly advancing in front of collapsing Afghan government forces. In June 2021, a US intelligence report predicted that the Afghan government would likely collapse within six months after NATO completed its withdrawal from the country. The report proved overly optimistic: by the second week of August, most Afghan provincial capitals had fallen into the hands of the Taliban and the Afghan National Army was in complete disarray, losing ground on all fronts. The falls of Mazar-i-Sharif and Jalalabad on 14 and 15 August respectively removed any possibility for the Afghan government to halt Taliban advance.