2015 was a big year for mergers and acquisitions, with global M&A activity exceeding $5 trillion, up 37% compared to 2014, according to Dealogic.

Acquisition news didn't slow down in December, with multiple major deals announced during the month. Keurig Green Mountain (GMCR.DL) will be acquired by privately held JAB Holding; DuPont (DD) and Dow Chemical (DOW) announced a blockbuster merger; Micron (MU -0.18%) is buying out a major source of DRAM chips; Newell Rubbermaid (NWL -1.42%) is acquiring consumer goods giant Jarden (NYSE: JAH); and Global Payments (GPN -2.23%) is adding scale by acquiring Heartland Payment Systems (HPY.DL).

Click through the following slideshow to learn more about these major acquisitions.

The next billion-dollar iSecret
The world's biggest tech company forgot to show you something at its recent event, but a few Wall Street analysts and the Fool didn't miss a beat: There's a small company that's powering their brand-new gadgets and the coming revolution in technology. And we think its stock price has nearly unlimited room to run for early in-the-know investors! To be one of them, just click here.

With Keurig Green Mountain struggling in 2015 as sales of its coffee machines collapsed, the huge premium JAB is paying for the company may seem like a bad idea. Here's a video explaining why JAB might have paid so much for Keurig Green Mountain.

The successful merger of Dow Chemical and DuPont will require the companies to beat back the antitrust issues that are sure to arise. If the deal does go through, a reasonable question to ask is how will the three companies spun off from the Dow Chemical and DuPont combination fare. Don't worry, the Fool's got it covered. 

Micron is suffering from DRAM oversupply, leading to selling prices falling faster than costs. The acquisition of Inotera should help Micron become more efficient, but after the company's latest earnings report, the worst for Micron may be yet to come.

Jarden may not be a household name, but many of its brands are, and its acquisition by Newell Rubbermaid will create a company with a vast catalog of popular consumer brands. Here's a video with more information about both Newell Rubbermaid and Jarden.

Payment processing is a business that requires scale, and Global Payments' acquisition of Heartland Payment Systems will create a much larger company. Here's a look at the deal between Global Payments and Heartland Payment Systems in more detail.