What were the reasons our forefathers divided the government into the legislative, judicial, and presidential?

The reason to divide into these 3 branches is because if they were all one, the nature of mankind, to combine and one emerge victorious as a dictator would cause competition. In one branch, there would be much competition in which one person would win and rule through a totalitarian regime. The four fathers were destined to prevent this, allowing this nation to hold unity through a democratic government. Since they are all seperate branch, each one checks on one other, system of checks and balances, which helps to keep order and purge any thoughts of dictatorship.