The Nielsen brand began in 1971 in Townsend, in the United States, founded by Helmar Nielsen. Ten years later he set up the German business with the entrepreneur Rainer Mönchmeier in Rheda-Wiedenbrück, and in 1984 the company bought its own aluminium press — the point at which it started manufacturing aluminium picture frames properly, in-house.
That German operation, Nielsen Design GmbH, still makes the Alpha profile in Rheda today, and supplies the UK through its English subsidiary. Nielsen describe themselves as the global market leader in aluminium picture framing — their words, not an independent measure, but the reputation among framers is real enough.
One point of confusion worth clearing up: you may find American pages for "Nielsen Bainbridge". That is a separate business — its US operations were acquired by Crescent Brands in 2021 — and it is not where the frames sold here come from. Ours are the German-made European ranges.