What major turning points or changes of power happened in Afghanistan in the 1970s?

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.