Pretty sure it's not in the US, or at least can be halted by the disapproval of antitrust regulators.
For example: https://www.marketwatch.com/story/staples-office-depot-merge...
That's the key though, they can continue to try until someone sits up and takes notice. Depending on the regulatory climate at any given time a company will have varying degrees of success with this before they are stopped outright before buying any more competition. Either that or they suddenly start abusing their positions such that people/other companies complain enough for regulators to take notice of them.