The principle of division or separation of powers states that the power of a state has to be divided in three independent branches:
To ensure that none of the branches gathers enough power to overrule the others, a system of Checks and Balances is established, so that each power supervises the actions undertaken by the other two. For example, judicial review is a mechanism employed by the judiciary power in the US which enables to abolish laws and govermental actions if they are violating the Constitution.