At the end of World War II an unusual set of circumstance occurred. As part of German war reparations, all German patents were made public. This was done with the intention of helping allied industry, but the effect in the photographic world was to create a giant postwar Japanese photo industry.
The easiest way for most of the Japanese photographic manufacturers to get products to the market was to copy as closely as possible a German camera. Many of the smaller companies had actually been repair shops before the war which were familiar with the construction of the cameras, and most had experience fabricating hard to get parts.
Some of the smaller manufacturers initially built cameras in very small batches, which had to be sold to buy materials to build the next batch. This created some models that are extremely scarce today. Some of these manufacturers succeeded and grew, some merged with others, and some failed.
Two Japanese camera manufacturers built Leica-like cameras before the end of the war. Canon had built and marketed a camera inspired by the Leica in 1935. But they had gone to great pains to design around existing patents, and these early cameras did not take Leica mount lenses. They did not produce thread mount lenses until World War II, and the lenses made before about 1948 or so are not exactly the same thread pitch as the Leica lenses.
The other manufacturer was Kogaku Seiki which Nippon cameras. They began production of cameras for the Japanese war effort. They evolved into Nicca, which was bought by Yashica in 1958.
While Japan built a large number of Leica Copies (as well as copies of the Rolleiflex/Rolleicord and folding cameras), a small number of models were built in the US, China and even Europe. But the other major producer of Leica copies was the Soviet Union.
One of the problems encountered when talking about Leica copies is defining what qualifies as a copy, and what does not. Most of these cameras are not exact copies of any one model. As time goes by, and Leica changes their models, the Japanese must respond without violating new patents, and the Japanese usually improved the camera they initially copied, quite often making the change before Leitz did.
I define a Leica copy as a focal plane shutter 35mm rangefinder camera with interchangeable lenses in 39mm thread mount.