Final answer:
Federalism in the United States has become more centralized over time, with a significant increase in the role of the federal government in areas that were once the domain of the states.
Step-by-step explanation:
The statement that accurately analyzes how federalism has changed over time in the United States is that a) Federalism has become more centralized, diminishing the power of individual states. Over the nation's history, federalism has evolved significantly. Originally, a system of dual federalism meant that the state and federal governments operated independently within their own spheres of influence. However, the shift to a more centralized approach started to occur, particularly during the era of cooperative federalism when the federal government began to play a more active role in areas traditionally managed by the states. This continued with the introduction of block and categorical grants, which allowed for federal influence in state policy implementation, and even though there was a push for new federalism which sought to decentralize policy management, the trend has been generally towards an increase in centralized power.