Has it really? Even if that's been the goal at times, I doubt it's been consistent.
I mean, it's hard to view the early 1880s in that light, just as one example - that being the period the US navy was essentially all fifteen years or more out of date, and the army was very small indeed.
By "no power or group of powers" standards, that's an enormous oversight that comes to making a mockery of the concept of "making sure".
the short answer to your assertion
http://ndupress.ndu.edu/Portals/68/Documents/Books/grand-strategy-us.pdf
the longer more thorough answer to your assertion
http://www.amazon.com/American-Pend...=1449198862&sr=1-7&keywords=US+Grand+strategy
http://www.amazon.com/Nation-Builde...1449198862&sr=1-12&keywords=US+Grand+strategy
http://www.amazon.com/Historical-Fo...1449198887&sr=1-19&keywords=US+Grand+strategy
History also answers your assertion: Both the American Revolution and War of 1812 involved campaigns to dominate the Great Lakes and Mississippi basin. The Louisiana Purchase was entirely about ensuring dominance of the Mississippi. The Mexican War and Spanish American War were about eliminating rivals to power in areas of vital interest (Southwest US and Caribbean respectively)
World War I and World War II were to ensure that no power dominated Asia or Europe to the point were it could threaten (realistically) an invasion of the Western Hemisphere..
The Cold War was waged to prevent a Eurasian Power from dominating East Asia, Western Europe and projecting permanent power into the Western Hemisphere.
The Monroe Doctrine was less about altruism and more about making sure no more European powers built up a major base of power in the Western Hemisphere.
We tried to annex Canada twice not just because we think maple syrup is tasty but because a major power could (and twice did) use it as a springboard for invasion..
I could literally go on for pages
I remember owning a book (lost in a fire damn it) that discussed the Grand Strategy of the US in detail
1. Dominate North America
2. Dominate the Western Hemisphere
3. Insure no major power can build a navy (and thus invasion fleet and army) large enough to threaten objectives 1 and 2.
American military history is replete with examples of efforts to ensure those goals. When they are seriously threatened, the US actually takes military action.
While the British could build the fleet in the 1880, they could not field the needed army to threaten the American heartland (the Midwest) even with a full mobilization. So in the period 1870-1890, the US literally had no enemy capable of threatening objective one and it was not in the British interest to allow anyone to accomplish objective two. Eventually the British could no longer prevent the Americans from achieving their principal objectives. Although objective three is a common British interest as well (as a dominate power in Europe would invade the British first in order to carry out any realistic chance at threatening the Western Hemisphere.. you British are after all in the most important geographical position on the Atlantic Ocean Rim)