What important role do third parties often play in us national elections? (a) causing major parties to fight one another (b) breaking up major parties' dominance (c) challenging people with more choices (d)
generating malice for larger parties

B) breaking up major parties' dominance.

Explanation:

The United States has a two-party system. This means that two parties dominate the political arena: the Democratic Party and the Republican Party. However, third parties play an important role as well. In national elections, third parties often break up major parties' dominance. This is important, as it means that the presence of third parties helps keep the two party system in check and the parties accountable.

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