So I've been working on my first map now and it didn't come out as I expected. I am halfway now and it seems I will end up with ~50 territories. Although the map is designed to be for 1v1 it still seems a little small. So now I want to go and divide the territories I made into smaller ones. What is the best way to make the current objects that I have into smaller objects?

Use the intersection tool. Draw another territory over it, duplicate the Territory you want to have split up, then mark both and use intersection.
Now you still have the original one and the downsized. You can then duplicate the new one and exclude or "difference" it from the original one.

Thanks for the quick answer. I'll go try that out ;)

Easier way: draw a line above the territory along the border you want to create, select both and use the Division tool.