Companies have shored up their balance sheets during the crisis, with US companies in particular boosted by the cheap loans provided under the Federal Reserve's asset purchasing program, so there is more cash to spend.
There is also now more optimism about the global economic recovery. Continued low interest rates mean that borrowing to fund acquisitions is cheaper. And shareholder activism has reared up again. Noisy interventions from people like Nelson Peltz at Pepsi and Carl Icahn at eBay mean there is more pressure on companies to take action rather than maintain the status quo.
(Read more: Peltz, Pepsi duke it out)
The return to the M&A fray will also mean better paydays for the investment banks which advise on these deals. Morgan Stanley leads the global rankings so far this year by advising on transactions worth $159.6 billion, followed by JPMorgan and Bank of America Merrill Lynch, according to Dealogic.
- By CNBC's Catherine Boyle. Twitter: @cboylecnbc.
(Disclosure: Comcast is the owner of NBCUniversal, the parent company of CNBC and CNBC.com.)