What is one great obstacle preventing third parties from gaining equal footing with the democrats and the republicans?

Compared with the Democratic and Republican Parties, it's difficult for third parties to gain meaningful or significant media coverage.

Explanation:

The mainstream media doesn’t give enough coverage to third parties, preventing Americans from knowing more about their candidates.

There are various other parties that are not discussed in the media because they are not considered viable enough and because the election structure is dominated by the two-party system. Two other parties are the Libertarian Party and the Green Party.

they made rome the dominant power in the mediterranean.