http://en.wikipedia.org/wiki/Federalism_in_the_United_States

Do web searches on “Federalism” and “states rights” and you’ll find plenty.

Basically:

At the time of the Constitution’s adoption, states had much more relative power. The fear people were responding to was that of the centralized British power over the colonies. Greater independence of each colony was seen as a way of preventing tyranny. On the other hand, they needed a central government with some muscle to avoid the chaos of the Articles of Confederation era.

During the Great Depression, the Federal Government took over a lot of the direction and coordinated control of the Country. This increased after the Depression. The fear was that an uncoordinated collection of individual States couldn’t combat the Depression which was national. Federal Government could bring the resources to plan nationwide projects to bring jobs and prevent the conditions that caused the dust bowl and bank failure. Then came WWII which was a centralized effort. Then came civil rights which, if left to States, would continue a system of segregation and discrimination.

Reagan sought to return power to the states. Conservatives rejected federal regulations of the environment, on civil rights, on abortion, on workplace safety and business regulation in general. They figured that they’d be morel likely to have the business interests they favored operate without oversight if they could fight their battles state by state away from national attention.