Why did European colonization of Asia and Africa expand dramatically after about 1800?

By the 1800s, Europe had finally developed new ships, called caravels, that allowed easy and safe oceanic transport.

The countries of Europe had begun the age of exploration and they were intent to discover continents.

Europe was overpopulated and needed to send large populations of settlers to other places in order to survive.

All of these are correct.

The Industrial Revolution allowed them to develop more and better weapons, and signficantly increased their need for raw materials for factory production.