At one time, while GM assembled cars in most major markets, these operations were largely autonomous. After all, GM expanded outside the US more by acquisition than by organic growth. For example, it entered the UK market through the 1925 acquisition of Vauxhall, which had started producing cars over two decades before, in 1903. Similarly the core of its continental operations is Opel, which began producing cars in 1900 but was not purchased by GM until 1929, while it acquired the Australian firm Holden in 1931. The most recent such acquisition was in 2002, when GM took over the core operations of the Korean-based firm, Daewoo (which turned out its first motor vehicle in 1937, during the Japanese colonial era).
That is no longer the case; GM is now a global firm, rather than a collection of national operations. Beginning in the mid-1990s it began to focus more carefully on developing a set of core platforms to serve as the basis for the vehicles it manufactured around the world. The next step was to lessen duplication, reducing the number of platforms, and then creating engineering centers that concentrated on specific products. Holden in Australia worked on rear-wheel-drive cars (though those programs are currently in abeyance); Opel in Germany worked on compact and mid-sized cars. The US focused on light trucks and larger front-wheel-drive vehicles. Finally, Daewoo focused on subcompacts. And consistent with that, Vauxhall in the UK no longer develops its own product; instead its vehicles are all engineered in Germany.
The geographic lines reflect in part the nature of the markets in which the engineering takes place; Europe, not the US, is the core market for compact cars, while subcompacts are more important Asia, Eastern Europe and the developing world, where Daewoo's strengths lie. In the current global structure each of these design centers then works with the various regional and national operations (such as North America) to develop vehicles specific to those markets. In the US the new Aveo is from Daewoo, which now handles the Gamma II platform, while in 2005 the engineering of GM's Delta platforms (e.g., the Malibu) was centralized in Germany. Paralleling this development of "world" platforms is the globalization of GM's supply chain; companies that wish to sell parts to GM need to be able to work with the relevant engineering centers, and to be able to produce their parts in multiple regions.
So, can GM then sell off Opel, and remain an ongoing operation? GM will be beholden to the new owners for core vehicles, as it will lose all independent ability to engineer small and mid-sized cars. Opel's products are a real strength to GM; they are one core of its surge in China, where sales jumped 50% in April 2009, and are essential in the US as well if (when!) high gasoline prices return. Unless the purchaser of Opel cooperates wholeheartedly with GM — grudging fulfillment of a contractual obligation won't do the trick — then, sooner rather than later, GM will collapse.
Now such cooperation is not impossible. Fiat's revival under Marchionne was dependent on product engineered jointly with GM's Opel subsidiary. They can and have worked together successfully, culture clashes or no. Second, Fiat has no presence in North America, and so can only gain from continuing to develop vehicles for GM in its home market; Fiat is also weak in China, where GM is the market leader. (They do compete head-to-head in Brazil, where Fiat is the market leader.) Should Magna, the other bidder for Opel end up carrying the day, there in fact are no such conflicts, as it has no independent OEM operations.
Losing Opel does not necessarily spell the end of GM as an ongoing business. But any car company that ceases developing new product has in effect declared that sooner rather than later it intends to close its doors. GM truly is a global business, and splitting itself up puts all of the pieces at risk — including Opel — because they are no longer standalone operations. The German government is nervous contemplating Fiat as the new owner of Opel. It should in fact be nervous about anyone other than GM owning Opel — and Obama's car czars should be as well.