Why We Don't Have Tyranny.
First, We Have Federalism
Federalism is the seperation of powers between Central and State governments. This allows the states to make sure the Central government doesn't take over. It also allows the Central government to keep the states together and make sure they don't receive to much power. Between the two types of governments there are different powers. They both share the ability to tax, borrow money, set up, courts, and other things.
Thirdly, we have Checks and Balances
Checks and balances are the way of basically checking or moderating the other Central government branches. Checks and balances is also used to approve or deny what other branches are doing. All the ways the branches can "check" on each other are down below in the diagram.
Lastly, the more populated, bigger states, can't bully the less populated, smaller states
Allowing the bigger, more populated, states to overpower the littler, less populated, states could turn our government basically into a tyranny. The big states working together to vote on the same thing. The way we defend against this is by giving every state the chance to elect two senators. Only two. These two only get six years to run as a senator. Each senator has one vote.