What was the core business that made standard oil a horizontally integrated monopoly?

He bought another businesses and products in order to increase or expand his business further. Refining oil was the business that made the standard oil a horizontal monopoly.

The government was though against the illegal monopoly. He bought other businesses which decreased the cost of production. This helped him increase his profits and business to such an extent that there was no other competitor in the market.

It owned 90% of the oil refineries in United States. Hence explaining the monopoly.

the tariff was created to protect industry in the northern part of the united states. industries in the north were being driven out of business by imported goods that were priced at a low rate. the goal was to protect these industries   by taxing the goods.