Fountain pens, as we know them today, are an American invention. The first relevant patents on these devices were filed in the US, and the main successful companies belong to that country—we all know Waterman, Parker, Sheaffer, Conklin…
Some American companies created branches in Europe –Mabie Todd, Parker, Waterman—while some European companies started their activities—Simplo, Osmia, Pelikan… But the reference in quality was still American.
A Japanese Swan no. 5, not affiliated with the American-British company.
Japanese pen companies, on their side, became active in those same years, albeit with a less relevant American influence. And after nearly a century of manufacturing, these companies are among the most active in the world.
Nowadays, American companies have lost most of their luster after years of decline, and their past prestige in now in the hands of European, and mostly German, companies. It is worth to notice, too, how independent nib manufacturers are now German and how American companies buy them for their pens instead of looking for nibs in their own market.
In the meantime, Japanese companies continue making some of the most interesting pens, with the widest variety of nibs, in the market.
Three different music nibs by two different Japanese manufacturers: Platinum and Pilot. More information on chronicles Ongaku and Encore.
So, from my point of view, the reference of fountain pens has shifted from the US to Europe. But it should have moved in the opposite direction—to Japan.