Here in Pittsburgh, we have lots of "Let's go Steelers!" (and some diehards who also say "Let's go Bucs!", but they're dying out). What does that phrase even imply? I assume it's similar to "Go Steelers", which I'm also not sure of the implications. "Go Steelers... to victory!" is a very strange way to phrase the sentence. Does anyone know where this phrase comes from?
Usually, "Let's go [team name]!" is used for teams with two syllables in their names and "Go [team name]!" for teams with just the one. They are used to encourage the team to move and go for it, I suppose.
However, the song did not become famous until 2005.
I expect that the "Let's go [team name]" cheer and other variants came about after the cheer-and-clap from the song by The Routers became popular.
Formulas of the type "Let us do something" are as old as the world.
are standard formulas, a kind of imperative where the speaker includes himself, which in Latin grammar already had the special name hortative.
In the Bible, Genesis 1:26 God says: Let us make mankind in our image ...
And in the King James Bibel, in the story about the Tower of Babel, the people immigrated from the east said one to another:
As to "Let's go", this formula can be used in its literal sense at the beginning of a walk, but also metaphorically in all senses a special context may offer.