The Vietnam War was one of the most controversial wars this nation has even known. It started out being about democracy, or so the people thought, but it went downhill from there and by 1967 most Americans were so anti-war it wasn't even funny. What was funny though, is that it seemed that all of the artists had been against the war from the beginning.
The artists saw what was going on in the world, and they wanted to change it. They saw big problems being ignored, and they wanted to do something about it. They used their artwork to communicate their thoughts on the Vietnam war, because the institutes, they felt, were ignoring the problem. This was infuriating to many, many people.
"Art and Language" was a catalog art piece that went on display in a museum. It was an index of ideas - just the way that a business would have a catalog complete with cross references and footnotes - only all the pages in this index were blank - because it was about the ideas. This particular piece of artwork was meant as an absurd joke - it was created in order to show people that art existed in your mind. You didn't need a critic to tell you what an art piece was about, because you could figure it out yourself. It was a direct rejection of the traditional sense of art, proving to the world that the institutes of today were meaningless. There was more going on with the world than people wanted to recognize.
This "Art and Language" piece of conceptual art helped lead the way into even more conceptual pieces. Land art, feminism, etc.