We’re six years into a bull market, debt is cheap and plentiful and corporate merger activity is approaching record intensity.

So where are all the barbarians?

Leveraged-buyout artists - sketched so vividly in “Barbarians at the Gate,” the chronicle of the 1980s battle for RJR Nabisco – have been largely absent from the deal-making scene.

More than $2 trillion worth of mergers and acquisitions have been announced globally this year, about half of that for U.S.-based companies. Yet less than 1% of that deal volume involves private-equity buyers, who invest client capital and borrow heavily against it to purchase companies.

In 2007, at the prior peak of M&A before the crisis, some 7% of deals were leveraged buyouts.

Troy Gayeski, a partner and portfolio manager for alternative investment firm SkyBridge Capital, believes the dearth of LBOs is largely the result of stricter rules put in place following the financial crisis.

“The main reason is regulatory reform,” Gayeski says in the attached video. “It’s an unintended consequence of the disintermediation of the banking system from the capital markets.”

Along with higher bank capital requirements and restrictions on banks investing directly in private deals, “knock-on rules were written, though, that limit how much leverage LBO firms can get to take a company private.” In LBOs, bank loans are typically an important component of the financing, along with high-yield bonds and equity investment from the LBO firms themselves.

As a consequence, private equity funds - such as those sponsored by Blackstone Group (BX) and KKR & Co. (KKR) - are having a harder time making the math work in their favor as they seek attractive returns for their investors, which typically include pension funds and other institutions.

Of course, with stock prices up more than 200% since 2009, corporate valuations might also appear fairly rich to these LBO sponsors. Many of them were burned by top-of-market buyouts in the last cycle, such as Caesar’s Entertainment, which has sought bankruptcy protection.

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Private equity has instead been a big net seller of companies, having unloaded nearly half a trillion dollars worth of prior investments last year. They now collectively sit on about the same amount of “dry powder” – capital raised from investors that’s waiting to be deployed in new deals.

Meantime, Deutsche Bank researchers make the case that activist investors are today’s version of the hostile corporate raiders of prior cycles. These activists – which take a stake in a company and agitate for shareholder-friendly changes such as share buybacks or spinoffs – have three times as much capital under management as five years ago, and the number of companies they’ve targeted has more than doubled in that time.