The answer is:
tax on an imported good
provides government revenue
can cause other countries to impose tariffs
reduces monopoly behavior
Tariff is being done in order To make the price of imported goods become higher as they enter the local markets, and the income from tariffs would be allocated to the government budget.
Because tariffs tend to reduce other country's national income, they tend to retaliate and impose the same tariff to the products from our country. Since it makes the product become more expensive, it allow many local companies to compete with the imported products, which reduce monopoly behavior.