That's not the only way monopolies can form, but it's the easiest one for sure. My counterpoint is that without strong independent institutions preventing them

That's not the only way monopolies can form, but it's the easiest one for sure. My counterpoint is that without strong independent institutions preventing them, the companies themselves will enforce the monopoly using private security or police forces. If the government is too weak, the company will buy it. If there is no government, the company will form it's own government. Like company towns- that's the natural end state of an unregulated market. The biggest company in the area can just buy everything and make their own laws.