Unity through Federalism

I have read several references recently (see one here) that make the assertion that the US has been able to remain one nation (albeit forcibly) as long as it has because of its decentralised form of government. Federalism, and the residing of much power in the states, allows diverse interests and groups to coexist within a common framework. Commentators have asserted that if the US were a unitary state like France, internal pressures would tear it apart. This seems plausible to me. And if this is true, then to the extent that the US government continues to erode the powers of the states and assert all authority unto itself, does it not move the country ever closer to dissolution and toward its [the government's] own possible destruction?