During the 1970s, Afghanistan started out fairly stable but undeveloped. Early in the decade, it experienced a coup that led to reform efforts. However, the government that came to power after the coup lasted only about 5 years. After that, came a revolution that was then followed by a Soviet invasion of the country that lasted for the rest of the decade.
Up until 1973, Afghanistan was ruled by a king named Zahir Shah. In 1973, he was ousted when Daoud Khan took the country over while Zahir Shah was out of the country. Khan ruled until 1978 when he was overthrown in the Saur Revolution.
This revolution caused a fairly chaotic situation. It finally ended up with a fairly socialist government in power. It was in order to try to prop up this socialist government that the Soviet Union sent troops to occupy the country in 1979.