From 1929 until the 14th April 1978 Afghanistan existed as a no-aligned, secular Parlaimentary democracy.

Just been looking up this period on Wikipedia. As far as I can make out.

The first ruler in that period was Mohammed Nadir Khan he was assassinated in 1933.

Mohammed Zahir Shah takes over and appoints Sardar Mohammad Hashim Khan, one of his uncles as prime minister.

In 1946, he appoints another of uncles, Sardar Shah Mahmud Khan, prime minister. This PM did start an experiment allowing greater political freedom but he reversed it.

In 1963, Zahir Shah starts governing on his own, He actually does introduce a new constitution in 1964. With the king appointing one third of the deputies, the people electing another third and the remainder selected indirectly by provincial assemblies, this seems to be as democratic as it got.

In 1973 the former Prime Minister Mohammad Sardar Daoud Khan seizes power in a non-violent coup, He abolishes the monarchy, disposes of the 1964 constitution and declares Agfghanistan a republic. He appoints himself as president and prime minister.