Let’s stop and think for a moment. What does each part of this snippet mean?
What does “communications between the tribes of the New World” mean?
Well, it’s how people in one tribe managed to talk to another tribe (for instance, riding a long way on horseback to visit the other tribe and telling them what was going on).
What does “news of the Europeans’ barbarities” mean?
It’s a description of what the European settlers were doing, which was taking the land, destroying tribal settlements and killing lots of people.
What is meant by “the rapid spread of new conquests and settlements”?
It means the settlers were rapidly conquering native tribes and establishing new settlements across the land.