@Allan,
Indeed, so am I.
Good question – from my quick reading of Wiki articles:
SPI tried to expand its customer base with Lorimar Productions to produce the Dallas role-playing game based on the soap opera Dallas in 1980. The game proved to be an infamous failure, and Simonsen later remarked that the 80,000 copies printed were 79,999 too many.
SPI had shopped for venture capital providers to take advantage of the perceived expansion of the gaming market in the late 1970s. When the expansion did not deliver the expected higher profits, only higher sales, the money needed to be returned. First efforts led to discussions with Avalon Hill to merge with or acquire SPI, but that did not materialize, partially due to the increasing losses in cash for SPI thanks to the increases in costs from inflation and the decreases in revenue. AH did purchase five of SPI's titles, which helped with operational costs. However, more money was needed.
SPI negotiated a promissory note loan (at the time mentioned as $225,000 USD but here listed as $400,000 USD from TSR (the publishers of Dungeons & Dragons). The note was guaranteed by SPI's assets. SPI used the cash to pay their venture capitalists, and were broke but happy. However, less than two weeks later, TSR called in the note. SPI, with no cash available and no options to get the cash, were forced to give over their inventory stock to TSR in early 1982, and were effectively out of business. TSR originally claimed they acquired SPI, but as that would mean they also would be responsible for their debts, quickly changed that statement. Thus, SPI's assets—but not its debts and liabilities—were acquired by TSR in 1983.
With the quick collapse of the wargame market in the early 1980s, TSR published fewer and fewer simulation games and eventually all the magazines (except for Strategy & Tactics) were discontinued. TSR sold S&T's rights to 3W Inc (also known as World Wide Wargames) in 1987. 3W published the magazine from #112 (June, 1987) to #139; after 3W's Keith Poulter got out of the business, Strategy & Tactics was sold to Decision Games.
In 1982, Avalon Hill hired several ex-SPI staffers to set up Victory Games Incorporated, a wholly owned subsidiary. The subsidiary was disbanded in 1989.
Decision Games, a California company founded in 1988, now has the rights to most of the SPI backlist. [However there are no clues as to what is or is not included.]. List of articles at link
All the best
Ian