The 17th amendment allowed people to vote directly for their senator during the voting cycle. In the past our federalist system of government had the senators nominated by the governors of the states to better represent the interest of the states. Now the senators are voted on by the people like the house of represenative. This serves to better concentrate power on the national level disregarding issues of the states. 100 years ago, we as a society better identified ourselves by our state. Now the states are little more than vassels of the national government. this was not what the forefathers had in mind as a check and balance against a too powerful national government.
An educated populace is the best protection against tyranny by a central government.