There is not a specific antonym for diaspora, but the opposite of a diaspora would be the regrouping of a community or the coming together of a community. It could also be a renewal of a specific cultural group or ethnicity coming back together in a sort of revival of their culture.
Because his voyages began a period marked by European empire.
Answer:
Congress had exceeded its authority in the Missouri Compromise
Explanation:
The Court ruled in the Dred Scott decision that Congress had exceeded its authority in the Missouri Compromise because it had no power to forbid or abolish slavery in the territories west of Missouri and north of latitude 36°30′.