The fact that the us constitution provided for federalism and a system of checks and balances suggests that

Its writers were worried about a concentration of political power is the right answer.

The system of checks and Balances is of much importance in the Tripartite form of government. In order to limit one branch from taking too much power, the constitutional committee set up a system of Check and Balance. Hence, all the three branches (the Legislative, the Executive and the Judicially) of the system are induced to share power.