What is the significance of the Census? | Explained

When was the first Census conducted? What are the two phases of the current Census exercise? Why is caste going to be enumerated in the upcoming Census? Why are southern States and some of the smaller States apprehensive about the Census exercise?

​When was the first Census conducted? What are the two phases of the current Census exercise? Why is caste going to be enumerated in the upcoming Census? Why are southern States and some of the smaller States apprehensive about the Census exercise?