Why did the mongols see the need to kill almost all of the inhabitants of nishapur?

Mongols kill more than 1.5 millions of people of Nishapur due to Genghis Khan's conquest tactics during that time.
Before attacking a city, he always give the time for that city to surrender and serve him (and required to pay taxes) or he and his army will massacre all people in that city and loot them, and the people of Nishapur chose to stand up and put up a fight.

Gengis Khan needed this to conveys some points to other cities:
- His army has the destructive power that could cause serious damage to them.
- He is not playing around with his threat and set the nishapur as an example
- It also serves as psychological warfare for the other cities, because they will lose their willingness to fight Genghis Khan before it even started

 

1920 census

the census was scheduled for january the 1st, as the government believed that more farmers would be in their homes by that time instead of april. the census did not ask about unemployment, the number of children, and how long was a couple married were not taken into consideration. individuals were considered as residents of the places they normally slept, not the places were they worked at or visited.

2010 census

the census was scheduled for april 1st, 2010. it was the shortest census in history: it only contained 10 questions related to name, age, gender, ethnicity, relationship, and whether the citizen owned a home or rented one. the government launched a website in order to provide the citizens with information regarding the census. there were also "teach census weeks" in schools nationwide.

Ain the free market economic system the government is hands off from all supply and demand rates