Afghanistan was at one stage, a some-what stable country. However, during the Cold War, communists overthrew the Monarchy and implemented some very radical communist programs (including eradication of religion... In Afghanistan... An almost entirely devout Muslim country). This led to Mujahadeen and guerilla fighters taking up arms against the Afghan Communists which in turn, led to the USSR invading Afghanistan (to stop the in-fighting but also re-establish a new, more sensible Communist party).

A bit of revisionism going on here, the last prime minister of the monarchy, Daoud Khan himself overthrew the monarchy in 73 with a bloodless coup and sought closer relation to the Soviet Union, which poured more money into the country than any other before, erecting most of the modern infrastructure in the country, roads, waterworks, hospitals and schools at the forefront. He did so do distance himself from Pakistan, have a strong military ally to settle border disputes and link the progressivist policies initiated (and ultimately partially reversed due to their overreach eroding monarchic authority) by his uncle Mahmud Khan with a palpable developmental basis.

The Saur revolution begun when Daoud Khan started questioning Soviet motives for providing so much development aid and experts with no demands in return, eventually weakening it's ties to the Kremlin. This triggered the Soviet leadership to train and support communist forces in Afghanistan, culminating in his assassination. Ali Bhutto's role was not small either, he actively supported the involvement in Afghanistan to increase Pakistani influence and weaken it's neighbour.