Weller, Charles Edward. The Early History of the Typewriter. Chase & Shepard, printers, 1918. http://archive.org/details/earlyhistorytyp00wellgoog.

You can cross check the data in the typewriter database for most of the big US and European brands to see the slow merging and dying out of the typewriter through the late 60s and early 70s onward. See, for example, Royal: https://typewriterdatabase.com/royal.72.typewriter-serial-number-database which has buyouts and mergers listed at the top. The database also has a huge volume of references for how it was compiled which will give you additional history.

The early 70s saw a lot of plastic entering the space where more durable steel used to be. Most major US firms were shifting to electric after IBM in roughly 1961. Post war manufacture of machines picked up significantly in Italy, Spain, Holland, and even Wales which displaced some of the manufacturing in the US, where solid machines of the prior generation still worked and only needed servicing rather than outright replacement. (Planned obsolescence wasn't as much of a thing during the 30s and 40s, and in fact, [maintenance was heavily highlighted during the war](https://www.youtube.com/watch?v=ocdxgkxKAKo) when most US manufacturers ceased production of most models.) Eventually Japan displaced the business followed by India (which ceased in 2009) and China. Wrexham, Wales ceased manufacture of electronic Brother typewriters in 2012.

Ever decreasing costs of materials and manufacturing, improved manufacturing technology, increased competition in the space, combined with containerized shipping, competition from computers, etc. all contributed to the cheapening of the typewriter and hastened the death of manufacturing (though not the use) of manual typewriters.

Richard Polt's The Typewriter Revolution (2015) has a "microhistory" of typewriters in chapter 2 with references to some addition histories if you're interested.

Your question about Olympia manufacture dates (and more) can be found via: https://typewriterdatabase.com/olympia.61.typewriter-serial-number-database

x over it has a good two part series about the evolution of Olympias at:

https://xoverit.blogspot.com/2015/02/olympia-sm-series-part-1-1948-1964.html

https://xoverit.blogspot.com/2015/04/olympia-sm-series-part-2-1964-1980s.html