I know et voilà is a French interjection and means there it is.
It is very much used in the US. Why is the use of et voilà so popular in the US?
Which historical fact has made it so popular?
I don't know what's made it popular, but I am interested that there are many instances where people render it in writing as "wallah!" (cf. "Voilà! Ear spellings" link text) This suggests that people are not using it out of a sense of knowing what the French actually means, but as an idiomatic phrase.