[<< wikibooks] Budget Watch Collecting/Brief history of Waltham
The American Waltham Company was the first mass-produced watch, using interchangeable parts.  
In 1954, Waltham established a Swiss subsidiary, Waltham International SA.  Because of peculiarities of Swiss law at the time, they could not establish a wholly-owned subsidiary, and when American Waltham went bankrupt in 1957, the Swiss company remained independent.  As part of the bankruptcy proceedings, rights to the Waltham name in the US and Canada were sold as part of the assets, while the rights to the name in the rest of the world remained with Waltham International SA.  
Walthams sold in the US are inexpensive quartz watches, part of the MZ Berger company along with Elgin and Gruen
Walthams sold in the rest of the world (primarily Japan) are high-end, mostly mechanical, and marketed by Waltham International SA.  While Waltham International is a Swiss company, it is owned by a Japanese businessman.