Meaning of "back on the wagon"?

[pne]

In the recent episode of SinFest, Squigley says that he's "back on the wagon".

What's the significance of this phrase? I take it it's got something to do with drinking alcohol?

Comments

[liv]

I believe in late 19^th or early 20^th America, (but not during the Prohibition, obviously) there was a Temperance organization that used to go round towns preaching an anti-alcohol message (I think there was Christian content as well). And they had a wagon to carry all their stuff, I guess. So if you were 'on the wagon' it meant you'd taken their pledge to stop drinking.

That's off the top of my head, so you might want to look for a more reliable source.