Short answers, pulled from the story.
The Emirate of Afghanistan began in 1823 when the Barakzai dynasty seized control of Kabul from the fading Durrani Empire. This political shift occurred after the Battle of Nowshera on the 14th of March 1823 where Afghan forces lost the Valley of Peshawar to the Sikh Empire.
British troops occupied Kabul during the First Anglo-Afghan War to prevent Afghanistan from falling under Russian control and to keep the country within the British sphere of influence. They installed Shah Shujah Durrani as a puppet leader but withdrew unable to subjugate the country completely before Dost Mohammad returned to his throne in 1842.
The Treaty of Gandamak signed on the 26th of May 1879 allowed Britain to assume control of territories within modern-day Pakistan and Afghanistan's foreign affairs. The Durand Line established in 1893 cut right through historic Pashtun settlement regions creating lasting border disputes.
Dost Mohammad died in 1863 and was succeeded by his son Sher Ali Khan. Three years later his older brother Mohammad Afzal Khan overthrew him before dying of cholera in 1867.
Full autonomy came with the Anglo-Afghan Treaty of 1919 following the Third Anglo-Afghan War which lasted three months. This independence followed the assassination of Habibullah Khan in 1919 and the subsequent fight against Nasrullah Khan by Amanullah Khan.
The earliest records trace to triangular red and green military flags bearing words of the Islamic confession of faith along with names of four caliphs and verses from the Koran relating to holy war. The first use of a coat of arms on a flag occurred under Emir Abdur Rahman Khan as a solid black banner featuring a white emblem in the center.