Why did the population of the world fluctuate until 1750?

If we are talking about fluctuate in the senses of rising up and down constantly it's because many people after 1750 had lots of children and the population since has been rising rapidly. Before 1750 the population wasn't that big and many people died during childbirth as well as their child. So in conclusion it's because advanced medicine and more knowledge about childbirth were discovered and less people died during childbirth.

Explanation:

I think I explained it in there, have a great day! -ibuki