Why would the FTC and the Justice Department be concerned about the merger of two strong companies in a marke

with few competitors? What advantages could the newly-formed company have?

The FTC and the Justice Department would be concerned about an oligopolistic firm, or even monopoly forming.

Explanation:

A monopoly is a firm that becomes the only seller in a particular market, while an oligopolistic firm is one that is part of an oligopoly: a market that only has a few sellers.

Monopolies have a lot of market power: they can set prices higher than needed, or higher than they would be if there was competition. These higher prices affects consumers, and because the monopoly is the only seller, the consumers cannot turn to other firms.

An oligopolistic firm also has market power, not as much as the monopoly, but they still can make alliances with the other firms that are part of the oligopoly in order to set prices that are higher than necessary.

For this reason, the FTC and the Justice Deparment are concerned about corporate mergers, and they can stop any of these mergers if it results in the creation of a monopoly.

might be agreeing to participate ethically with other european nations in the slave trade

or notifying other european nations when taking possession   of african territories

what are you options