In the late 1700s and early 1800s, colonialism and mercantilism began to change. Why?

the main reason was it was during this time the foundation was laid towards the industrial revolution, as new technologies and innovations were made to enable mass production and develop factories and an economy that was completely different from the existing one.

moreover, the revolutionary events such as the french revolution, american revolution showed that pure colonialism and the mercantilist way of economy was not working anymore.

moreover, the development of share markets, bonds, banks and financial institutions along with new and complex ways of financial instruments and derivatives, the  foundation for the industrial and financial capitalism was laid.  

Explanation:

new evidence is discovered.

oversights and errors are corrected,

new technology is applied to evidence.