What issues led to the colonist’s declaring independence?

The extremely strict monarchy of Brittan, mostly due to its extremely narrow and strict religion and its rules. That is why they settled in the first place.

They declared independence because of the insane taxation Brittan was forcing on them.

The first issue that led to colonists declaring independence was all of the taxes. Taxes began with the stamp act, which put a tax on all stamps. The next tax was the stamp on all paper products. Another tax was the tax on all imported goods, especially tea. Another issue that led to colonists declaring independence was the fact that the British Parliament did not listen to the colonists or give them some basic rights. 

A. southerners underestimated republicans eagerness to end slavery.