Megacorporations to their greatest extent

Vast and powerful vertically and/or horizontally integrated corporations developed in Japan (the zaibatsu, later keiretsu) and South Korea (the chaebol). At times only a handful of these companies, corporations, or conglomerates owned and controlled the majority of each nations economy. They have lost some power since their peak in the 80s or 90s, but still hold enormous sway. Samsung, Sony, Mitsubishi are examples.

Could one corporation have possibly gained even more power, to the point of over half the Korean or Japanese economies being under the control of a single board of directors? Are there other countries where this might be more likely? What would be the effects of a single organization having monopolies on transportation, banking, insurance, electricity, communications, and the majority of industrial goods?
 
A regional rather than national example, but when I moved from Toronto to New Brunswick I was surprised that something like 10-15% of the province's labour force worked for the Irvings. The Irving family owns almost 100% of the forestry, transportation, petroleum refining and distribution, shipbuilding and much of its potato and other agricultural processing.
 
Did that have any really obvious or strange effects?

Canada has fairly robust antitrust laws, korea in the 50s not so much.
 
When I visited South Korea last year, I was amazed at how big and how diversified Lotte was. I've never seen one company have such a big influence over a country before (including during my visit to Japan). It felt like they owned half of Korea.
 
At one point Nokia was like 20 % of Finlands economy.

The best way to get megacorps is to have producers of finished goods focus on getting their entire supply chain under their own control, from mine to sale, all in one hand, all profits in one company, from there on it's just continued growth into other sectors using the available basic resources or buying new ones.
 
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