Checks and balances.
While separation of powers does split up the powers of the government it does not establish ways to keep the three branches’ powers even. That is what checks and balances does. Each branch can “check” another branch’s actions and can act to prevent an action from going through.
For example: congress (legislative branch) can aim to pass a law but the president has the power of veto. The president “checks” the legislative branch’s power by vetoing a law they may not like or think is unfair. Without this check on the legislative branch’s power congress would be able to pass any law they want thus making them more powerful than the executive and judicial branch.
