Why did Japan dominate the DSLR( Digital Single Lens Reflex) market?
Japan:
Canon, Nikon, Sony, Olympus, Pentax, Panasonic.
Other:
Leica, Kodak…
They did not share the market.
Japan has been dominating not just the digital SLR camera market
In 1959, the Nikon F was introduced and it was immediately picked up by photojournalists.
Prior to then, most of us used Leica rangefinder cameras and if we were on a budget, we used Nikon rangefinders.
A Nikon F cost around $200 with a 50 mm f/1.4 lens. A Leica M3 at that time costs around $465 and a 50 mm f/2.0 lens was another $285.
Pentax also had a 35 mm SLR, the Pentax Spotmatic had a built-in lightmeter, something that Nikon did not have until 1962 and no through the lens light meter until 1965
The cost of these high quality cameras being relatively inexpensive, amateurs started buying cameras made in Japan. One of the least expensive and popular cameras was the Petri. Under $100 in 1968
Leica, Rollei, Hasselblad, Zeiss Ikon, Voigtlander and Alpa were the highest quality cameras from Europe. The inexpensive cameras like Praktica and those being produced in the Soviet Union of that time were either not robust enough for amateurs or just not available.
As I hope you can see, Japans leadership in digital SLR development and sales started many decades ago and are just the result of blending new technology with the nearly bullet proof platforms of nearly 50 years ago.
Leica and Hasselblad are still in the domain of the wealthy and their cost has to be justified by a photographer when they have to include the cost of those cameras and associated lenses. (My bookkeeper went nuts when I purchased a Nikon D3 for just over $6,000. Can you image what she would have said had I proposed to buy a Hasselblad H3D plus at least three lenses (about $75,000?
Because they already owned the 35mm SLR market.
In the early 1960s, you could get an Exa (Budget Exacta) with a four speed shutter, non-return mirror and waist level viewfinder, for the same price as a Pentax S1 (H1 in the US) with an eleven speed shutter, instant return mirror and pentaprism.
Japanese SLRs were as reliable as their European counterparts (more so in the case of the Zeiss Contarex), but often better specified, and generally considerably cheaper.
Zeiss (Contax) went into partnership with Yashica, Leica targetted the luxury market, and everybody else was unable to compete.
If you are old enough to remember that they dominated the film SLR market before that, you wouldn't be surprised.
Because they dominated the camera market before digital cameras existed.
The why and wherefore is a long story. But essentially it's because the best European camera manufacturers made very expensive cameras (Leica/Hasselblad/Rollei etc etc), so to get in on the market the Japanese copied (or reverse engineered) these types of cameras, such as range finders, TLRs, and SLRs, and mass produced them cheaply so that everyone could afford one.
Back then after the WWII, Japan was like how China is now for cheaply manufacturing goods. Things have changed, but Japan still dominates the camera market.
If you go back further in time, Kodak did once dominate the camera market when they mass produced the first popular consumer camera, the Box Brownie in the early 1900s.
Quality / cost…