Most "Zeiss" cameras were produced at the beginning of last century by Zeiss Ikon AG, which was created in 1926 by the Carl Zeiss Foundation as a merge of several companies, including ICA, Contessa-Nettel, Ernemann and C.P. Goerz. In 1945 (after the war) Zeiss Ikon was split into two parts, the Eastern and Western.
The Western part was licensed to produce cameras under the same Zeiss Ikon name in the western world, so its cameras are also listed under Zeiss Ikon. Unfortunately, it ceased production in 1972, and was split up and sold to several other companies.
The Eastern part, VEB Zeiss Ikon, also produced some cameras under the same names, for distribution in the part of Eastern Europe occupied by the USSR. This company is listed in this catalogue as Zeiss Ikon VEB. This is a matter of individual preference, since some Price Guides suggest listing this company under the Pentacon name in virtue of the fact that it was merged into VEB Pentacon later.
Now, with respect to the other part of Zeiss world: Carl Zeiss Jena, which was producing cameras as early as 18th century. After the war this company was divided into two parts as well: Eastern VEB Carl Zeiss (known for Werra cameras), and western Carl Zeiss (which was not producing cameras). After a long history, these two companies are now back together, operating under the name of Carl Zeiss.
The arrow pointing to the "year" line shows the point at which the company was divided, created or merged with other company. This graph doesn't, however, track the origins of external companies like Voigtländer. Click on the image to view a larger version.