OS/2 preceded Windows, so I'm not really sure how your history makes sense. Windows was Microsoft stabbing IBM in the back and making a clone of OS/2.
Windows 1.0 was released 20 November 1985.
Windows 2.0 was released December 9, 1987.
As to the whole backstabbing thing:
The collaboration between IBM and Microsoft unravelled in 1990, between the releases of Windows 3.0 and OS/2 1.3. During this time, Windows 3.0 became a tremendous success, selling millions of copies in its first year. Much of its success was because Windows 3.0 (along with MS-DOS) was bundled with most new computers. OS/2, on the other hand, was only available as an expensive stand-alone software package.
Volumes have been written about this, but key was that Microsoft had more at interest than selling Windows - Microsoft was selling a platform for its Office products, and maybe a chance at file format lock-in for business applications. That meant they wanted as many copies out there as possible. IBM, on the other hand, wanted to sell overpriced PS/2 machines, and had no interest in cannibalizing this by bundling OS/2 with the likes of Dell, Gateway, Compaq, and Packard-Bell, whereas all of these companies desperately needed someone to supply an OS to complete a turn-key product. Microsoft did a simple business assessment, and concluded they could team up with the clones and blow the doors off the market if they weren't bound somehow to promoting IBM's hardware.