What is the primary reason to have three branches of government?

I know that in the U.S.A. we have three branches of government. The legislative, judicial, and executive. I think the main reason why we have them is because we cant just have one person deciding the laws, it needs to be approved by many people. Congress can even pass a law if the president veto's it!

- Middle schooler

i believe it was the shinto

1 problem today is that it caused to much crime americans are born with freedom and liberty and not being restricted to things causing lots of crimes because there free until proven guilty and commit a crime

the pursuit of order has only made people hate order causing race profiling and   more

3 it has to much liberty the liberty is to much because it causes to much crime and aswell hacking and letting hackers open to numerous things such as stealing cards and more