how has the idea of federalism changed over the years?

Answer 1

Somewhat. Federalism, at it's most basic, is simply the idea of splitting the governing duties between the national government and state governments. That definition has not changed.

However, over the years, the prevailing opinion over whether the States or the Federal Government is responsible (or has power over) certain things has changed dramatically.

The biggest changes would be the Civil War amendments (13th, 14th, and 15th), which allowed the federal government to impose an end to slavery, force a new definition of citizenship upon the states, and enact Bill of Rights from the US Constitution on the States (previously, the Bill of Rights only applied to the Federal Government). This, combined with the income tax and an expansive use of the Commerce Clause (which empowers Congress "To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes."), has greatly expanded federal power at the expense of the states.

Many things that we accept as being within the federal governments scope now would never have been allowed under the Constitution and Bill of Rights as originally ratified.

Answer 2

Evolution Of Federalism