Question

Lord Acton, a British historian of the late 19th century, said that, "Power tends to corrupt; absolute power corrupts absolutely," suggesting that a person's sense of morality lessens as his or her power increases.

How do you know that power was what corrupted ?  Perhaps they were always evil?  

Answer 1

Power brings out the true character of a person. They might not exhibit their reality when not in power because they cannot cover up their mistakes or make people deal with them. But once a person comes to power, they would get authority to take decisions and to make people listen to them and to influence the authorities which would make them bring out their reality . They show how corrupt they can be and how they can use their power to escape. Hence power always do not make a person corrupt. They might be the same evil always and just shows it out as they have power.