Some unions have created all-powerful corporations.
Ever since East Indian and New East Indian companies merged in 1708, the world's leading companies have joined forces to cut costs and increase market share. This year, for example, AT&T and Time Warner joined forces to raise capital of more than €100 billion, a move that risks putting AT&T in the face of "frightening" debt.
However, former AT&T chief strategy officer John Stankey, now WarnerMedia's chief executive, expects the risk to pay off big as the company looks to reshape the media landscape. Here we tell you what some of the biggest business mergers of all time have been:
Citicorp Group and Travelers Group
Citicorp and Travelers Group merged in 1998, forming Citigroup, the largest financial services company on the planet. Banking institutions ran into trouble with regulators and had to sell several key assets to get the green light for the move.
RFS Holdings and ABN Amro
A consortium made up of leading financial institutions Royal Bank of Scotland (RBS), Fortis and Santander came together in 2007 to acquire Dutch bank ABN Amro for €98 billion, beating the British Barclays' bid. The company was dissolved, but resurfaced in 2010 when the Dutch government bought the opera house from Fortis.
Exxon and Mobil
The €77 billion merger of energy titans Exxon and Mobil in 1998 created the world's largest corporate entity and brought together the two key pieces of John D. Rockefeller's Standard Oil, which dissolved in 1911 after a remarkable institutional action against business monopolies.
Anheuser-Busch InBev and SAB Miller
Budweiser maker Anheuser-Busch InBev was already the world's largest brewer when it took over competitor SAB Miller, which has been listed on the London Stock Exchange since 2015. The giant deal was ratified for €130 billion.
Dow Chemical and DuPont
In a merger of two behemoths, US chemical giants Dow Chemical and DuPont teamed up in 2015 in a deal worth €130bn, an amount similar to what Anheuser-Busch InBev paid for SAB Miller.
Verizon Communications and Verizon Wireless
Verizon Communications is involved in the second largest telecommunications merger in history. It first bought the Vodafone Group in 2013 to gain full ownership of Verizon Wireless and bring the two companies together. In total, the deal cost more than 130 billion euros.
Pfizer and Warner-Lambert
Prior to its mergers with Pharmacia Corporation and Wyeth several years ago, Pfizer acquired rival Warner-Lambert in the biggest such deal ever. The pharmaceutical giant shed nearly €120 billion in 1999 to close the deal.
AOL and Time Warner
The disastrous merger of AOL and Time Warner in 2000 has been described by Time Warner CEO Jeff Bewkes as "the biggest mistake in corporate history." The €165 billion link failed to capitalize on the strengths of the two companies and ended with outrageous losses of billions of their respective stock and market values.
