I need one example of real history where federalism limited the power of the government??

Answer 1

Both of the current examples are wrong. Federalism means that there are certain aspects of life that the U.S. Government cannot regulate and MUST leave to the states. Oftentimes, the Supreme Court will declare a law unconstitutional because it was not enacted purusant to Congress's "enumerated powers" in Article I of the Constitution. Congress can't make any law it want, but can only make a law pursuant to the powers dedicated to it (Usually article I, section 8 of the Constitution, although there are other sources of Congressional power, such as the Fourteenth Amendement "enabling clause")
This was an issue prior to the New Deal. But here's the most recent example:
In the 1990s Congress passed a law that made a federal penalty to possess guns near school zones. They tried to enact the law pursuant to the "commerce clause" (Congress may regulate interstate commerce, most guns travel in interstate commerce, threatening students harms interstate commerce etc.)
The Supreme Court struck down the law as unconstitutional, finding that Congress didn't have the authority to enact that federal law pursuant to the Commerce Clause. The regulation of guns near schools wasn't substantially related to the traveling of the guns in interstate commerce, nor did you have to prove the that guns traveled in interstate commerce. The case was United States v. Lopez. (See link below.) If states want to enact such a law pursuant to their general "police powers," they're free to do so, but that law was outside the particular scope of Congressional authority.

Answer 2

It lead to the Civil War.

States rights butted heads with the national government and it lead to war.

Answer 3

Right to bear arms was invested in an individual. That right is now being taken away by mindless do gooders in Chicago and San Francisco