Dealmaking was up 37% from 2014, and it was more than double the volume of 2009. Perhaps the most interesting thing about this year’s deal boom is that nothing seemed to be able to stop it. Typically, deals tend to follow the stock market. As stocks go up, executives get more optimistic and do more deals. But even as the market faltered in the summer, and worries about the global economy erupted, the pace of corporate combinations continued; in fact, it appeared to speed up.

The record amount of deals could have to do with low interest rates. That allowed for cheap financing and tepid economic growth, sending corporate executives looking for ways to expand and back door ways to boost earnings. Below are the biggest deals of the year and their size (including debt):

1 Pfizer/Allergan - $160 billion

It was the biggest and most controversial deal of the year. There aren't a lot of synergies between Pfizer and Allergan, outside of dodging Uncle Sam. Combining with Allergan (AGN)—technically, Allergan is buying Pfizer (PFE)—will save the drug giant at least $1.2 billion a year in U.S. taxes, and possibly as much as $3.3 billion, according to one tax expert's estimates. It will also likely save Pfizer $21 billion in deferred taxes it will now never have to pay. Perhaps that's why they call it a super inversion. The Pfizer deal caused Hillary Clinton and other presidential hopefuls to say they would do something to stop such tax-driven deals.

2 AB InBev/SABMiller - $117 billion

AB InBev (AHBIF) and SABMiller (SABMILLER-PLC) will still have to shed a good deal of their U.S. beer business to make the deal work. But that's okay. This deal is all about becoming the leading beer seller in emerging markets, where the real growth opportunities are. The deal will also create a mountain of debt.

3 Royal Dutch Shell/BG Group - $82 billion

In April, Royal Dutch Shell (RYDAF) decided to take advantage of the drop in the values of fellow oil companies and buy BG Group. It's unclear how wise that decision was. Oil prices have continued to drop. Originally, Shell said the deal made sense even if oil prices dropped to $70 a barrel. They recently dipped to $34. The deal gets Shell into the liquified gas market, as well as the offshore oil fields of Brazil. The move has been blessed by regulators and is likely to get approved by shareholders. Now Shell just needs to make the math work. It recently said it would cut back its capital spending in 2016.

4 Charter/Time Warner Cable - $80 billion

After Comcast called off its deal to buy Time Warner Cable (TWC), John Malone's Charter (CHTR) swooped in. The deal will create the second largest cable company in the U.S., with 17 million video subscribers, behind only Comcast with 22 million. The deal still needs regulatory approval, which could stretch well into 2016.

5 Dow/DuPont - $68 billion

With hedge fund activists on both sides, Dow Chemical (DOW) and DuPont (DD) finally met in the middle. The two companies decided in December to hook up in a complicated deal that will combine the two companies, but then break them up shortly after into three separate companies. The companies' CEOs Dow's Andrew Liveris and DuPont's Ed Breen say the deal will save the combined firm $3 billion a year in costs, but it's hard to see how turning two companies into three will do that, other than if these two storied science giants dramatically cut back on what they spend on research. It appears they are likely to do that, leading many to criticize the deal. DuPont has already said it will cut 1,700 workers in its home state of Delaware ahead of the deal.