For Altria and Philip Morris International, breakin' up may have been too hard to do.

A decade after going their separate ways, the two tobacco giants announced this week they are considering a merger.

The potential merger would end years of speculation on whether the companies would eventually reunite. Marlboro-maker Altria spun off PMI in 2008 to help the international business grow and shield it from the U.S. regulations and litigation.

If they recombine, the newly formed company would be a $200 billion behemoth that dwarfs the market value of its next-largest rival, British American Tobacco, by about $120 billion. But a lot has changed in the decade since the two split, and Big Tobacco can no longer pin its future on the cigarettes its empire was built.

Only problem: The two main sectors Altria is eyeing for growth — vaping and cannabis — are new fields beset by regulatory challenges. Electronic cigarettes, in particular, are already hamstrung by investigations, litigation and accusations of intentionally hooking underage kids on addictive nicotine pods.

Selling cigarettes is still an incredibly profitable business — albeit a shrinking one. Global smoking rates are declining as health officials across the globe sound alarms over its long-term health consequences. In response, tobacco companies are developing other ways to deliver nicotine that are less carcinogenic, including e-cigarettes, heated tobacco products and oral-derived nicotine pouches that don't release the toxins in tobacco known to cause cancer.

Merging Altria and PMI's businesses would allow the combined company, which already sell the same cigarette brands, to work together on new products, or at least that's the thought, according to people familiar with the company's thinking. A deal may not materialize, the companies warned. And if one is reached, the company's boards, shareholders and regulators would need to approve.

But Moody's analyst Roberto Pozzi said the combined company could use its heft to invest in new products, generate more profit and better manage the risks that come with entering new markets.