Vertical integration is when one company controls all aspects of an industry, like how Carnegie Steel owned the mines, the boats that transported ore to the smelting factories, the refining factories, all the transportation needed to get their product from place to place, the production of raw materials to keep their factories running, etc. - I recommend
reading up on it.
I would defend this by pointing out that it can save the producer TONS of money by avoiding middlemen and contractors, which then translates to savings for the end consumer (in theory, anyway). The downside to this is that the monopoly might not actually pass the savings on to the consumer.