They always seem like a good idea at the time, but mergers and acquisitions have a notoriously high fail fate and research shows between 70% and 90% end in tears. Here we look at the most traumatic tie-ups in history and what happened next...

Almost a decade in the planning, the merger between the Pennsylvania and New York Central Railroads in 1968 turned out to be a total fiasco, despite starting out $5 billion in the black.

The two companies had vastly different business cultures and pretty much hated each other. They made very little effort to integrate operations, personnel and assets, and didn't even bother to carry out the integration plan that had been devised.

Fragmented and rudderless, the newly formed Penn Central Transportation Company was unable to reverse a decline in passenger numbers and freight volumes, and just two years down the line in 1970 the firm went bust, filing for what was then the largest bankruptcy in US history.

Desperate to get into the burgeoning internet industry, AT&T, which had already made several unsuccessful attempts in-house to join the IT revolution, forked out $7.4 billion (£5.5bn) in 1991 to buy computer company NCR.

AT&T was confident the hostile takeover would be a success, but in spite of funnelling billions of dollars into the flagging company, the new AT&T Global Information Solutions division just couldn't turn a profit.

By 1996, the ill-judged purchase had cost AT&T over $5 billion (£3.7bn). Increasingly exasperated by the division's dismal performance, AT&T management conceded defeat and spun it off that same year. Let's hope AT&T's $85 billion (£63.6bn) takeover of Time Warner, which has just been approved, doesn't go the same way.

In 1994, cereal and snack conglomerate Quaker Oats snapped up Snapple for a steep $1.7 billion (£1.3bn), rather a lot more than analysts believed the drinks company was worth. Having made a mint following its acquisition of Gatorade in the late 1980s, Quaker Oats were sure it was on to a winner.

The company couldn't have been more wrong. The market for 'new age' drinks, such as Snapple, was already slowing down when Quaker Oats made the purchase, and its attempts to boost sales fell flat.

Several marketing missteps later, Quaker Oaks decided to do away with Snapple, which was dragging the entire conglomerate down. The drinks company was sold in 1994 to Wendy's parent firm Triac for just $300 million (£225m).

A transatlantic love affair that turned sour, Germany's Daimler had high hopes for its $36 billion (£30bn) merger with Chrysler. The link-up should have provided Daimler with access to the lucrative US market, and Chrysler with quality but affordable German-made parts.

As it turned out, Daimler's efforts to access the US market were scuppered by intense competition from Asia, while the reluctance of the Mercedes-Benz division to supply parts to Chrysler, which it considered an inferior, mass-market marque, killed any teamwork.

In 2007, less than 10 years after the acquisition, Daimler sold Chrysler for just $7.4 billion (£5.5bn). "We obviously overestimated the potential of synergies," said company CEO Dieter Zetsche after the sale went through.

At the height of the dotcom bubble in 1999, Yahoo bought entrepreneur Mark Cuban's Broadcast.com – fittingly on April Fool's Day – for a ridiculously overpriced $5.7 billion (£4.3bn), 57 times its revenue.

Like a basic combo of YouTube and Netflix, the internet audio and video broadcaster was one of the first to offer users streaming content, but the service was beset with a number of insurmountable problems.

Videos took ages to load and constantly froze – this was the era of dial-up after all – and content was limited, which turned off users. Yahoo threw in the towel in 2002, and the service has since been quietly discontinued. The only winner in the whole debacle was Mark Cuban, who made a fortune from the deal.

Another epic fail for Yahoo, GeoCities was the third most-visited website when it was snagged by the web services giant in 1999 for a bloated $3.6 billion (£2.7bn), and its future looked very bright indeed.

Yet despite being a trailblazer in user-generated content – GeoCities was one of the first platforms that allowed users to create their own websites – its popularity declined sharply in the early noughties.

Yahoo's efforts to monetise the platform alienated users. When MySpace came along in 2003, GeoCities' days were seriously numbered. By the mid-2000s, GeoCities was looking decidedly passé. Instead of overhauling the site, Yahoo left it to die a slow death. The web-hosting service was finally shut down in 2009, although it's still available in Japan.

Citicorp's $140 billion (£104.63bn) merger with Travelers in 1999 should have united the banking giant with the insurance titan and merged their services seamlessly to create one of the world's premier financial institutions.

In actual fact, the two entities were seriously incompatible and even John Reed, the executive who masterminded the deal, has called it a mistake. A toxic combo of overinflated costs, management conflict and outdated tech brought the bulging company to its knees.

By March 2009, the Citigroup share price had plummeted from a high of $569.39 (£425.60) in 2000 to an embarrassing $10.30 (£7.70), the bank had received an enormous government bailout, and it had fallen behind financial institutions it once eclipsed such as JP Morgan Chase.

Remember Netscape? AOL made the first of two catastrophic takeovers when it purchased the pioneering web browser in a deal worth $10 billion (£7.5bn), which closed in March 1999.

With massively differing corporate cultures, the two companies had a nightmare making the union work. Meanwhile, Microsoft's Internet Explorer (IE) was establishing itself as the go-to browser. IE's superior interface, usability and speed trounced the competition. By 2000, Microsoft's browser had a 95% market share.

Netscape was disbanded in 2002, but AOL continued to release versions until 2008. These days, the once-mighty web browser is long gone, but Netscape continues to live on as Firefox, which uses its source code.

As disastrous takeovers go, the acquisition of Time Warner by AOL in 2000 takes some beating. This marriage of new and old media cost a bewildering $165 billion (£123.60bn) and should have blended the best of both companies to create a multimedia force to be reckoned with.

In reality, things worked out very differently. The internet side of the business lost significant market share when high-speed broadband arrived on the scene, and the mega-merger failed to capitalise on the two firms' strengths.

The hook-up ended up wiping billions off the linked company's value, and has been described by Time Warner CEO Jeff Bewkes as “the biggest mistake in corporate history”. Gerald Levin, the executive who presided over the deal, apologised in 2010 for “the pain and suffering and loss that was caused”.

Throwing obscene sums of money down the drain yet again, Yahoo went on another ill-advised spending spree in 2004, splashing a hefty $627 million (£468m) to bag French price comparison site Kelkoo.

The web services giant was looking to improve its targeted advertising offerings in Europe and pair advertisers with individual products, something which Kelkoo had an excellent track record in doing. At the time the acquisition seemed like a perfectly sensible, smart move.

Sensible and smart it definitely wasn't. Kelkoo's popularity began to wane as users defected to faster and more comprehensive price comparison sites. Less than three years after purchasing the Paris-based site, Yahoo sold it on to a British private equity firm for less than $115 million (£86m).

In 2005, Rupert Murdoch's Newscorp parted with $580 million (£434m) to get its hands on MySpace which, as you may fondly recall, was the hottest and most popular social media site at the time.

Newscorp was looking to cash in on internet advertising and use MySpace to drive traffic to its newspaper sites. A foothold into the wonderful world of the internet, MySpace seemed like a sure-fire bet. Then Facebook happened.

The competing social media site exploded in popularity. MySpace began losing users in their droves. Despite several redesigns, the exodus couldn't be stopped. An unloved shadow of its former self, MySpace was offloaded by Newscorp in 2011 for a paltry $35 million (£26m).

Retail's largest merger, hedge fund-owned Kmart acquired Sears in 2005 for a whopping $11 billion (£8.2bn). The link-up was meant to revive both brands and save the new parent firm Sears Holdings millions of dollars thanks to economies of scale and improvements in the supply chain. If only.

Sears Holdings' sales have fallen every year since the merger with analysts putting the blame on a variety of factors, from Sears' confusing brand identity to a lack of meaningful investment in the merged company.

Struggling to survive, Sears Holdings is in the process of closing hundreds of stores in a bid to keep its head above water. The firm's share price has dropped from a high of $144.09 (£107.67) in 2007 to a pathetic $2.14 (£1.6bn) in June 2018, and the prospects for the business are anything but rosy.

Telecoms giant Sprint bought the equally huge Nextel in 2005 in a deal worth $36 billion (£26.39bn), creating what both companies hoped would be an unstoppable wireless phone juggernaut, but the newly formed Sprint Nextel Corporation was problematic from the get-go.

Integrating the companies' networks and services proved to be a major headache, and the respective firms' management teams were just as incompatible, making the challenge even more difficult.

On top of this, lacklustre products, worsening customer service and intense competition from the likes of AT&T hammered the business, and in 2008 the company was forced to write off $29.7 billion (£22.2bn) of the $36 billion (£26.9bn) deal.

The powers that be at Toshiba must rue the day they acquired US nuclear energy company Westinghouse Electric back in 2006. The Japanese conglomerate's foray into the American nuclear power industry was going to diversify its North American operations.

Instead, the $5.4 billion (£4bn) deal almost brought down the entire group. In 2015, Westinghouse Electric paid over the odds for nuclear reactor manufacturer CB&I Stone & Webster, but neglected to take into account cost overruns.

The screw-up, which came to light in 2016, cost Toshiba $6.4 billion (£4.78bn) and shaved 40% off its share price. Toshiba finally offloaded Westinghouse earlier this year, and has been busy selling off other assets to balance the books.

When Bank of America's acquisition of ailing mortgage lender Countrywide was finalised in 2008, the banking institution's bosses thought they'd lucked-out big-time by paying just $4.1 billion (£3bn) for the firm. Little did they realise the purchase would end up costing the bank dear.

Bank of America had become America's number one mortgage lender at the worst possible time, just as the entire industry was facing collapse. Now liable for Countrywide's past wrongdoings, the financial institution had to pay out billions of dollars in subprime crisis-related legal fees and settlements.

In fact, Bank of America is estimated to have lost a staggering $50 billion (£37.4bn) and counting as a direct consequence of the misguided merger. No wonder the deal has been dubbed the worst finance industry acquisition of all time.

But the award for the most ill-judged takeover in UK and Australian history goes to Wesfarmers. Keen to enter the UK market, the Perth-based retailer acquired British DIY chain Homebase via its subsidiary Bunnngs in 2016 for $453 million (£340m).

The Australian firm made error after error with its new company, from firing every single senior manager to ditching the chain's profitable home furnishing lines, which only served to alienate much of its customer base.

Needless to say, sales nosedived. In February, Wesfarmers was forced to write off the value of the company to the tune of $729 billion (£547bn), and the Australian retailer has since washed its hands of Homebase, selling the chain earlier this month for just $1.33 (£1).

Now read: The biggest business mergers of all time