Technically, Adobe InDesign predates QuarkXPress because it is derived from PageMaker, the first desktop publishing program. PageMaker outsold QXP for many years, but QXP became the industry standard largely because PageMaker didn't break away from its original design. QXP meanwhile had "lifted" certain aspects of desktop publishing software from programs such as Ready, Set, Go! and became the easiest, yet most powerful, desktop publishing program available. While QXP generally has larger market share than InDesign, the latter made a number of innovations that QXP raced to keep up with.
Programmer Paul Brainerd decide to take advantage of the graphical user interface of the Apple Macintosh that was introduced with a legendary advertisement during the Superbowl in 1984. Windows didn't exist yet, so there was no GUI on the PC. In 1985, Brainerd introduced PageMaker 1.0 through his company, Aldus. It changed the publishing world at every level. Newspapers eliminated the entire composing room where workers previously had cut and pasted sheets of printouts on layout paper called flats, then photographed them with room-sized cameras to make printing plates. Once this all could be done on a computer, it eliminated the need for these workers and editors and paginators took over. PageMaker mimicked the way newspaper composers laid out pages. Other companies raced to get into the desktop publishing market. QuarkXPress was introduced two years later in 1987.
QXP vs. PageMaker
Until 1999, when InDesign was introduced by Adobe, the market had shifted largely to QXP. This happened after QXP was updated in 1996 to version 3.3 and PageMaker simply didn't keep up. InDesign built market share slowly, but got a leg up when QXP was left languishing for several years until version 7 was released. By then, InDesign had become part of the Adobe Creative Suite, designed to be integral with all the other Adobe products including Illustrator and Photoshop. PageMaker, now owned by Adobe, gradually was phased out.
InDesign has the advantage of working well with the other Adobe products. Before QXP did, InDesign allowed the importation of graphics with Layers and allowed the user to directly output files to PDFs. It also introduced drop shadows for graphics and text long before QXP. QXP 6 also was very glitch-prone, which allowed InDesign to make strides in the market. Since most publishing companies, especially newspapers, already used Illustrator and Photoshop, it made sense for many of them to switch to InDesign. Adobe also took advantage of the fact that many were switching by making it possible to use the command keys people were used to in QuarkXPress.
No matter how good InDesign is, however, QXP still has the market, largely because it was there first. When workers first had to learn desktop publishing for the creation of newspapers or books or magazines, QXP was there. Just like in the Mac vs. PC debate, even though the Mac may be easier to use, crashes less and isn't susceptible to viruses, PC users don't like to switch because they already know the PC and Windows system. People familiar with QXP feel the same way. InDesign may be more elegant in certain ways and it may work better directly with Illustrator and Photoshop, but they are used to QuarkXPress. Especially for those who work with desktop publishing programs for their living, the slow-down factor of learning InDesign can be frustrating, even though the same command keys will work.
In the end, InDesign and QuarkXPress both are solid desktop publishing programs that essentially do the same thing: allow you to design and layout anything from a newsletter or poster to a book or magazine. Both have a full range of publishing and design tools and both allow you to work relatively quickly.