Microsoft in the 1990s, had tried to find a replacement for DOS partnering up with IBM. Commodore had the Amiga, Atari had the Atari ST, and Apple had the Macintosh and their operating systems were better than DOS. So out of an advanced DOS project came OS/2 and then the GUI for OS/2. IBM had their own OS/2 and Microsoft had their own OS/2 as well.
Microsoft was working on Microsoft OS/2 NT 3.0 when they broke off from IBM, and then renamed it Microsoft Windows NT 3.1 using the Windows 3.X GUI. Microsoft also pushed Windows 3.0 and 3.1 that loaded on top of DOS. IBM had OS/2 2.0 that had WIN-OS2 to run 16 bit Windows apps. Then companies quit making OS/2 native apps and made 16 bit Windows apps instead because OS/2 could run them as did Windows.
The big blow to IBM was Microsoft's Windows Tax to OEMs, that is based on how many computers they made, even if Windows was not installed on the new PCs. So if someone wanted to install IBM's OS/2 or Next's Nextstep for Intel chips, or BeOS for Intel, they still had to pay Microsoft the Windows tax. This forced OEMs to preinstall Windows, because they already paid for it with the Windows tax.
So it was a combination of OS/2 running 16 bit Windows programs and companies not wanting to make an OS/2 native version, and Microsoft marketing Windows to be used instead of OS/2 by bundling it with every OEM PC sold, that stabbed IBM in the back over OS/2.
Yes, Microsoft in the 1990s were ruthless and even bundled Internet Explorer with Windows 95 OSR and Windows 98 that got them investigated by the DOJ for antitrust issues.