I'm bumping this one to the top of the list because it's more current than ever. Another one from olden times at The Valve (November 2006).
Word up:
It is impossible to read the compositions of the most celebrated writers of the present day without being startled with the electric life which burns within their words. They measure the circumference and sound the depths of human nature with a comprehensive and all-penetrating spirit, and they are themselves perhaps the most sincerely astonished at its manifestations; for it is less their spirit than the spirit of the age. Poets are the hierophants of an unapprehended inspiration; the mirrors of the gigantic shadows which futurity casts upon the present; the words which express what they understand not; the trumpets which sing to battle, and feel not what they inspire; the influence which is moved not, but moves. Poets are the unacknowledged legislators of the world.
–Percy Bysshe Shelley, A Defence of Poetry
For the last three years or so I've been telling myself - and a few others as well - that anime and manga will do for the visual culture of this century what African-American music did for the musical culture of the last century:
Provide idioms that are adopted everywhere and adapted for local use.
I've now added graffiti to the list - not graffiti in general, but the kind of grafs I discussed in Shrine of the Triceratops, the contemporary sort that originated in America in the late 60s and early 70s and was then assimilated to hip-hop culture. The purpose of this post is simply to play around with the notion that grooves, grafs, and toons have been providing and will continue to provide the basic transnational idioms of musical and visual culture in the global age. This is an exercise in throat-clearing, thinking out loud, sizing things up.

Outa' Here
Grooves
African American music - Europe meets Africa in North America - has been around the longest. I've seen a reference to minstrelsy in India in the mid-19th century, but have been unable to follow up on it. For the most part it seems to me that this florescence happened mostly in the 20th century; first jazz, then rock and soul (with the blues tagging along), and finally hip-hop. Each time a new set of idioms arose, they went international. By the late 20th century all the major idioms were performed in all continents (Antarctica excepted, though I suppose some of the folks working there might play a little something sometime - surely someone has taken a guitar or a harp there) and local hybrids have given rise to so-called world beat music - a marketing category for fusions of this or that African American idiom with anything else.
Why did this happen? Well, there is good old Western Imperialism organizing a international flows of goods, services, and ideas. But that just gets the music around; that doesn't make it stick, much less flourish and breed. For that the only reasonable answer is that it is locally attractive, not to everyone (it's not even that attractive at home), but to enough people to make a home for it. Why is it so attractive? The answer to that is not obvious, so let's leave it alone for now (see here for some fairly standard speculation).
Grafs
Then we have graffiti. The standard story is that the modern idiom arose in Philadelphia and New York City in the late 60s and early 70s with simple “tags” aerosoled in publicly visible places. Ornate elaboration started in Philadelphia and then spread to New York, which it achieved its first flourishing on the sides of subway cars. As that died in chemical baths, the idiom spread to any and all available surfaces. When hip-hop came along in the late 70s, it picked up graffiti as one aspect of general hip hop culture and hence graffiti made the world trip along with hip hop. (At least I think that's what happened. I don't know how far it had spread before hip-hop picked it up.)