Actually, this came from one of Gordon Sinclair's daily radio commentaries on CFRB in Toronto, a gig he held pretty much unto his death - he was "the Walter Cronkite of Canada", but his was primarily a radio career. I think it got a lot of positive phone calls from listeners, and op-ed-ed (I'm guessing in The Globe and Mail, but I should look it up). Byron MacGregor, the news director at Windsor Top 40 flamethrower CKLW, was so taken by it, that he read it on the air. Then someone at Detroit's Westbound Records (across the river from Windsor, and the home of Funkadelic and The Ohio Players) liked it, and released a 45 (called "The Americans") with MacGregor intoning the words, and with "America the Beautiful" playing in the background. It became a big hit record; MacGregor even made an appearance on The Midnight Special, a late-night rock-music program, performing it. Around this time, Avco Records released a similar 45, with Sinclair himself on "lead vocals".

The original commentary was on June 5, 1973, during his 11:50 AM time slot. (IIRC, he also had a straight-news 10 AM slot). In 1973, a lot of things were going wrong in the United States. Sinclair's words were, obviously, a swipe at growing anti-American-ism around the world, in the face of the US' botched Vietnam War (and peace) policy, and the rise of the "non-aligned" nations of the Third World to a position of power, at least at the United Nations (aside from the Security Council, where the US has a veto).

But it was also a pep talk to Americans; Sinclair had listeners in the border regions of New York, so it was literal in that sense, but aimed at Americans in general. The post-Bretton-Woods floating of the dollar allowed it to sink in value against other major currencies. Inflation was beginning to be a problem in general; meat prices spiked a bit, giving rise to meat-extender products like Lipton's Make-A-Better-Burger, and Hamburger Helper, a product which has survived to our modern day, and to families having meatless days or dinners, vegetarians out of economic necessity, rather than choice. The Yom Kippur War and subsequent Arab oil embargo sent gas prices soaring, and there was rationing (you could get gas on odd or even days, and in some places, there was a limit on how much gas you could get, if you were willing to wait in a long line to pump it); though Sinclair's original commentary predates the war and its fallout, the MacGregor and Sinclair 45s came out early in 1974, so you can add the petroleum and Watergate miasmas to the mix of woes besetting the US at the time. Plus, of course, all the ongoing cultural-upheaval fallout of the 60s.

"The Americans" was the most unlikely of hit records, but there were a few others, inspired by its success; Johnny Cash's soliloquy "That Ragged Old Flag" comes to mind - it, too, was a big hit, but not as big as "The Americans".

RealAudio of Sinclair's broadcast:
A 6½-years-later version (1979, a year that was very 1973/4), by Sinclair: