Corporate mergers - like marriages - can result in the whole being stronger than its parts -- or they can end in utter disaster. The IT industry has suffered its share of disastrous marriages. Here are the worst of the worst. (Previously: HP and Autonomy, Google and Motorola)

# 3 - Nokia & Microsoft

In Steve Ballmer's 15-year tenure as Microsoft CEO, he got a lot of things right: several highly successful product launches, significant increase in shareholder value, and a few acquisitions that proved quite valuable to the company.

However, he will likely be remembered as the man who drove the most catastrophic merger in the company's history.

Microsoft has always struggled in the mobile space. The company was early to the game with Windows CE and Windows Mobile (far earlier than Apple and Google); but it was late to adopt the mobile developer ecosystem and "app store" strategies of its competitors.

In November 2010, following the surprising success of the iPhone, the company introduced Windows Phone, which abandoned much of the legacy 32-bit Windows code in previous mobile releases. Windows Phone featured a brand-new user experience that has evolved into the Universal Windows Platform (UWP) that powers Windows 10 and runs on all Windows devices.

However, Microsoft needed OEM hardware partners, who were reluctant to take on the risk of an unproven software platform when they were already enjoying success with Android.

One partner that had taken that risk was Nokia, which -- under the leadership of former Microsoft exec Steven Elop -- was itself being forced to transform. Competitors such as Samsung and Apple were eating Nokia's lunch in the company's stronghold EMEA smartphone markets.

Nokia made some impressive Windows Phones during its partnership with Microsoft, but it was not able to bring itself back to profitability. By 2013, in fact, the company was considering a move to Android and had even built prototype devices running Google's software. If that move had succeeded, Windows Phone would have been left with no OEM support. It would have effectively been a death sentence.

Ballmer, looking to solidify his legacy, saw a potential synergy. Nokia, with its native manufacturing capability and R&D, could be Microsoft's solution to ramping up their mobile presence, in addition to providing an essential distribution channel via previously existing carrier relationships.

In September of 2013 Microsoft bought Nokia's mobile business for over $7 billion. This included the acquisition of most of the company's assets in Finland as well as manufacturing capacity in Asia, along with 24,000 employees. Crucially, it didn't include the potentially valuable Here maps business, which the Microsoft board reportedly refused to go along with.

Many analysts questioned why Microsoft had not simply contract manufactured the phones, negotiated the carrier relationships on its own, and hired engineering talent for much less money. The analysts turned out to be correct. Microsoft struggled to consolidate its development platform over two consecutive OS releases on the desktop and its mobile OS, and was unable to attract the developer and carrier partnerships needed to make the new Lumia phones successful.

Since Ballmer's departure from Microsoft in 2014, under the leadership of its new CEO Satya Nadella, the company has laid off over 15,000 employees, the majority of whom came in from the Nokia acquisition.

In all, more than 20,000 jobs at Microsoft will have been cut once the restructuring is complete.

In 2015, the company was forced to write down the acquisition of Nokia's mobile and services businesses for $7.6 billion.

While Microsoft has recently announced several new Windows 10 Mobile phones, and has committed to the continued development of the platform, it has yet to solidify its carrier relationships or attract the developer attention it needs to compete favorably with devices running Apple's iOS or Google's Android.

Although the pieces are now finally in place for the "One Windows" that could finally make Microsoft smartphones and the modern Windows development platform successful, the company could have saved itself a huge amount of money and heartache if it did the work in-house, rather than by a failed and costly acquisition.

#2 - AOL & Time Warner

Facing challenges from the growing Internet/Web and broadband industry in the late 1990s that was encroaching on its bread and butter dial-up services and "walled garden" of content, on-line services provider America Online pursued a strategy of re-invention as a content and broadband giant by purchasing Time Warner in the year 2000 for a whopping $164 billion.

The merger, executed by AOL CEO Steve Case and Time Warner CEO Gerald M Levin, turned out to be a total fiasco, with the new company unable to capitalize on Time Warner's strengths. Total subscribers of AOL went from an estimated 30 million at the height of its popularity to less than just over 5 million in 2007, with no significant quarterly growth since 2002.

The company's market valuation had plunged significantly from a high of $240 billion to $1.73 billion as of February of 2012.

In 2009, shortly after appointing a new CEO, Tim Armstrong, AOL announced it would spin off Time Warner into a separate public company, ending a fruitless eight year relationship.

AOL has since gone on a New Media purchasing spree, including Patch, TechCrunch and The Huffington Post, which joins their other New Media properties such as Engdaget which it acquired as a result of its Weblogs, Inc. purchase in 2005.

The result of these New Media mergers has been something of a disaster in and of itself.

After re-organizing all of its new media properties under one roof and appointing Arianna Huffington as its leader, TechCrunch became the subject of a highly publicized internal power struggle.

TechCrunch's founder Michael Arrington came into conflict with Huffington over journalistic ethics when he unveiled a plan, with AOL's backing, to start a venture capitalist fund to invest in the very same sort of companies which he writing for TechCrunch chronicled.

After weeks of public blog posts criticizing his employer and the media circus surrounding him, Arrington was terminated. This resulted in the departure of several members of TechCrunch's staff, including Paul Carr, one of its most popular writers, as well as the company's CEO, Heather Harde.

In June of 2015, AOL was acquired by Verizon for $4.4 billion. Only time will tell if this second marriage will be more fruitful.