How is federalism a tool for the protection against "majority tyranny" and therefore a protection for the minority?

Federalism means the way of government where there are various levels of government. As different level government system is more accessible for general people where they can say what they want or express their opinions about something being right or wrong. So in my opinion for the most part Federalism is a tool for the protection against "majority tyranny" and therefore a protection for the minority. To explain this in an example, if a state banns all the women to be employed at any level, the federal government will intervene and stop this unjust decision, or vice versa. 

Iwould say either b or ci could be wrong let me know